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Dr. K
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    • Biography
    • PhD
    • University of Michigan
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    • with Famous Mathematicians
    • Museum of Math (MoMATH)
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    • US Army Service
    • Bicycles and Motorcycle
    • NYC Deli Cats
  • Tricks
    • Number Guessing
      • Guess Your Number
      • Honest Liar
      • 2-Digit Mind Reader
      • Cubic Root Calculation
    • Check Digits
      • Check Digit Algorithms
      • Check Digit Anchor Charts
      • Check Digit Worksheets
      • Check Digit Calculator
      • 8-Digit Barcode
      • 12-Digit Barcode (UPC)
      • 13-Digit Barcode (ISBN)
      • 14-Digit Barcode
      • 15-Digit Credit Card (American Express)
      • 16-Digit Credit Card (VISA & MasterCard)
      • 17-Digit VIN
      • 18-Digit Barcode
    • Calculator Tricks
      • 3-peat 777
      • 6-peat 777,777
      • 9-peat 777,777,777
      • Devil's 666
      • 3-Digit Repeat 123 123
      • 4-Digit Repeat 1234 1234
      • 5-Digit Repeat 12345 12345
      • Guess Your Birthday
      • 6 Times Even
    • Pretend Mental Math
      • Addition 18
      • Calendar Math Tricks
    • Ancient Calculators
      • Multiplication By Lines
      • Roman Multiplication
      • Lattice Multiplication
      • Napier Bones Multiplication
      • Slide Rules
      • Abacuses
      • Division By Dots
    • Binary Holes Sorting
    • Magic Card Tricks
      • 4th Card
      • 1/7
      • Four Sevens
      • 2 More & Get You To 20
    • Math Talks
    • Full Precision Calculator
  • Puzzles
    • Wordle, Nerdle, and More
    • SIMP
    • Transum Puzzles
    • Grid Puzzles
      • Calcudoku
      • Skyscrappers
      • Kubok
      • Kakuro
      • Capsules
      • Products
      • Different Strokes
      • Thermometers
      • Arrows
      • Borderlands
    • Assembly Puzzles
      • Wooden Egg
      • Moses' Snake Cube
      • 6-Piece Ball
      • Soma Cube
    • Sliding Puzzles
      • 15 Puzzle
      • Setting Sun Puzzle
      • Colors Disk Puzzle
      • Ball Colors Puzzle
    • Arranging Puzzles
      • Cruiser 4-Piece Wooden
      • Hercules Puzzle
    • Math Blanks Puzzles
      • Magic Triangle
      • Bar Model Fractions
      • Pyramid Addition
      • Not Too Close
      • Hexa-Trex
      • Visual Logic
      • Other Math Puzzles
    • Kinesthetic Puzzles
      • String Handcuffs
    • Art Puzzles
      • Mondrian Math
    • Verbal Logic Puzzles
      • Riddles
      • Emperor's Proposition
      • Alliteration Multiplication Word Problems
    • Counting Puzzles
      • How Many Triangles?
      • How Many Squares?
      • How Many Rectangles?
    • Code Breaking Puzzles
      • Mastermind
    • Optical Illusion Puzzles
  • Games
    • 2-Player Games
      • Connect 4
      • Cat and Mouse
      • NIM - Sea Shells
      • NIM - Matchsticks Pyramid
      • Intransitive Dice
      • Make 15
    • Multi-Player Games
      • Rummikub
      • Blokus
      • Pit
      • SET
      • On The Dot
  • Rubik's Cubes
    • Layer By Layer Method
    • CFOP Method
    • Cubing Culture
    • Mosaics
    • Patterns
    • Calendar Cubes
    • Fruit Cubes
    • Mirror Cubes
    • Giant Cubes
    • Void Cubes
    • Pyramix Cubes
    • Megaminx Cubes
    • Egg Cubes
    • Ivy Cubes
    • Skewb Cubes
    • Oblique Prism Cubes
    • Gear Cubes
    • NxN Algorithms
    • Robots
    • Other Cubes
  • Math Everywhere
    • Math on TV
    • Math In Books
    • Math Augmented Reality
    • Invisible Math
    • Betting Odds in Sports
    • NFL QB Passer Rating
    • Math Memes
    • Math Fails
      • Tonic Water Calories
      • Gym Membership Plans
      • Bloomberg Spending
      • 3 + Dozen = 15
  • Bitcoin
Dr. K
  • Home
  • About
    • Biography
    • PhD
    • University of Michigan
    • Family
    • My Dog, Yeti
    • with Famous Mathematicians
    • Museum of Math (MoMATH)
    • StreetSquash Harlem
    • US Army Service
    • Bicycles and Motorcycle
    • NYC Deli Cats
  • Tricks
    • Number Guessing
      • Guess Your Number
      • Honest Liar
      • 2-Digit Mind Reader
      • Cubic Root Calculation
    • Check Digits
      • Check Digit Algorithms
      • Check Digit Anchor Charts
      • Check Digit Worksheets
      • Check Digit Calculator
      • 8-Digit Barcode
      • 12-Digit Barcode (UPC)
      • 13-Digit Barcode (ISBN)
      • 14-Digit Barcode
      • 15-Digit Credit Card (American Express)
      • 16-Digit Credit Card (VISA & MasterCard)
      • 17-Digit VIN
      • 18-Digit Barcode
    • Calculator Tricks
      • 3-peat 777
      • 6-peat 777,777
      • 9-peat 777,777,777
      • Devil's 666
      • 3-Digit Repeat 123 123
      • 4-Digit Repeat 1234 1234
      • 5-Digit Repeat 12345 12345
      • Guess Your Birthday
      • 6 Times Even
    • Pretend Mental Math
      • Addition 18
      • Calendar Math Tricks
    • Ancient Calculators
      • Multiplication By Lines
      • Roman Multiplication
      • Lattice Multiplication
      • Napier Bones Multiplication
      • Slide Rules
      • Abacuses
      • Division By Dots
    • Binary Holes Sorting
    • Magic Card Tricks
      • 4th Card
      • 1/7
      • Four Sevens
      • 2 More & Get You To 20
    • Math Talks
    • Full Precision Calculator
  • Puzzles
    • Wordle, Nerdle, and More
    • SIMP
    • Transum Puzzles
    • Grid Puzzles
      • Calcudoku
      • Skyscrappers
      • Kubok
      • Kakuro
      • Capsules
      • Products
      • Different Strokes
      • Thermometers
      • Arrows
      • Borderlands
    • Assembly Puzzles
      • Wooden Egg
      • Moses' Snake Cube
      • 6-Piece Ball
      • Soma Cube
    • Sliding Puzzles
      • 15 Puzzle
      • Setting Sun Puzzle
      • Colors Disk Puzzle
      • Ball Colors Puzzle
    • Arranging Puzzles
      • Cruiser 4-Piece Wooden
      • Hercules Puzzle
    • Math Blanks Puzzles
      • Magic Triangle
      • Bar Model Fractions
      • Pyramid Addition
      • Not Too Close
      • Hexa-Trex
      • Visual Logic
      • Other Math Puzzles
    • Kinesthetic Puzzles
      • String Handcuffs
    • Art Puzzles
      • Mondrian Math
    • Verbal Logic Puzzles
      • Riddles
      • Emperor's Proposition
      • Alliteration Multiplication Word Problems
    • Counting Puzzles
      • How Many Triangles?
      • How Many Squares?
      • How Many Rectangles?
    • Code Breaking Puzzles
      • Mastermind
    • Optical Illusion Puzzles
  • Games
    • 2-Player Games
      • Connect 4
      • Cat and Mouse
      • NIM - Sea Shells
      • NIM - Matchsticks Pyramid
      • Intransitive Dice
      • Make 15
    • Multi-Player Games
      • Rummikub
      • Blokus
      • Pit
      • SET
      • On The Dot
  • Rubik's Cubes
    • Layer By Layer Method
    • CFOP Method
    • Cubing Culture
    • Mosaics
    • Patterns
    • Calendar Cubes
    • Fruit Cubes
    • Mirror Cubes
    • Giant Cubes
    • Void Cubes
    • Pyramix Cubes
    • Megaminx Cubes
    • Egg Cubes
    • Ivy Cubes
    • Skewb Cubes
    • Oblique Prism Cubes
    • Gear Cubes
    • NxN Algorithms
    • Robots
    • Other Cubes
  • Math Everywhere
    • Math on TV
    • Math In Books
    • Math Augmented Reality
    • Invisible Math
    • Betting Odds in Sports
    • NFL QB Passer Rating
    • Math Memes
    • Math Fails
      • Tonic Water Calories
      • Gym Membership Plans
      • Bloomberg Spending
      • 3 + Dozen = 15
  • Bitcoin
  • More
    • Home
    • About
      • Biography
      • PhD
      • University of Michigan
      • Family
      • My Dog, Yeti
      • with Famous Mathematicians
      • Museum of Math (MoMATH)
      • StreetSquash Harlem
      • US Army Service
      • Bicycles and Motorcycle
      • NYC Deli Cats
    • Tricks
      • Number Guessing
        • Guess Your Number
        • Honest Liar
        • 2-Digit Mind Reader
        • Cubic Root Calculation
      • Check Digits
        • Check Digit Algorithms
        • Check Digit Anchor Charts
        • Check Digit Worksheets
        • Check Digit Calculator
        • 8-Digit Barcode
        • 12-Digit Barcode (UPC)
        • 13-Digit Barcode (ISBN)
        • 14-Digit Barcode
        • 15-Digit Credit Card (American Express)
        • 16-Digit Credit Card (VISA & MasterCard)
        • 17-Digit VIN
        • 18-Digit Barcode
      • Calculator Tricks
        • 3-peat 777
        • 6-peat 777,777
        • 9-peat 777,777,777
        • Devil's 666
        • 3-Digit Repeat 123 123
        • 4-Digit Repeat 1234 1234
        • 5-Digit Repeat 12345 12345
        • Guess Your Birthday
        • 6 Times Even
      • Pretend Mental Math
        • Addition 18
        • Calendar Math Tricks
      • Ancient Calculators
        • Multiplication By Lines
        • Roman Multiplication
        • Lattice Multiplication
        • Napier Bones Multiplication
        • Slide Rules
        • Abacuses
        • Division By Dots
      • Binary Holes Sorting
      • Magic Card Tricks
        • 4th Card
        • 1/7
        • Four Sevens
        • 2 More & Get You To 20
      • Math Talks
      • Full Precision Calculator
    • Puzzles
      • Wordle, Nerdle, and More
      • SIMP
      • Transum Puzzles
      • Grid Puzzles
        • Calcudoku
        • Skyscrappers
        • Kubok
        • Kakuro
        • Capsules
        • Products
        • Different Strokes
        • Thermometers
        • Arrows
        • Borderlands
      • Assembly Puzzles
        • Wooden Egg
        • Moses' Snake Cube
        • 6-Piece Ball
        • Soma Cube
      • Sliding Puzzles
        • 15 Puzzle
        • Setting Sun Puzzle
        • Colors Disk Puzzle
        • Ball Colors Puzzle
      • Arranging Puzzles
        • Cruiser 4-Piece Wooden
        • Hercules Puzzle
      • Math Blanks Puzzles
        • Magic Triangle
        • Bar Model Fractions
        • Pyramid Addition
        • Not Too Close
        • Hexa-Trex
        • Visual Logic
        • Other Math Puzzles
      • Kinesthetic Puzzles
        • String Handcuffs
      • Art Puzzles
        • Mondrian Math
      • Verbal Logic Puzzles
        • Riddles
        • Emperor's Proposition
        • Alliteration Multiplication Word Problems
      • Counting Puzzles
        • How Many Triangles?
        • How Many Squares?
        • How Many Rectangles?
      • Code Breaking Puzzles
        • Mastermind
      • Optical Illusion Puzzles
    • Games
      • 2-Player Games
        • Connect 4
        • Cat and Mouse
        • NIM - Sea Shells
        • NIM - Matchsticks Pyramid
        • Intransitive Dice
        • Make 15
      • Multi-Player Games
        • Rummikub
        • Blokus
        • Pit
        • SET
        • On The Dot
    • Rubik's Cubes
      • Layer By Layer Method
      • CFOP Method
      • Cubing Culture
      • Mosaics
      • Patterns
      • Calendar Cubes
      • Fruit Cubes
      • Mirror Cubes
      • Giant Cubes
      • Void Cubes
      • Pyramix Cubes
      • Megaminx Cubes
      • Egg Cubes
      • Ivy Cubes
      • Skewb Cubes
      • Oblique Prism Cubes
      • Gear Cubes
      • NxN Algorithms
      • Robots
      • Other Cubes
    • Math Everywhere
      • Math on TV
      • Math In Books
      • Math Augmented Reality
      • Invisible Math
      • Betting Odds in Sports
      • NFL QB Passer Rating
      • Math Memes
      • Math Fails
        • Tonic Water Calories
        • Gym Membership Plans
        • Bloomberg Spending
        • 3 + Dozen = 15
    • Bitcoin

Check Digit Algorithms

Check Digit Anchor Charts

Check Digit Worksheets

Check Digit Calculator

8-Digit Barcode

12-Digit Barcode (UPC)

13-Digit Barcode (ISBN)

14-Digit Barcode

15-Digit Credit Card (American Express)

16-Digit Credit Card (VISA & MasterCard)

17-Digit VIN

18-Digit Barcode

drkmath777@gmail.com

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