Last update: December 14 2014

Prime Hexagon Spiral


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  • Primes are colored red.
  • Press & drag to pan the diagram.

 

How it works

  • Starting with 1, the numbers spiral around a hexagon so that they're broken up into 6 rows.
  • All primes other than 2 & 3 end up in rows 1 & 5.
  • Numbers in rows 1 & 5 that are not prime are divisible by previously found primes, the first of which is 25 (5x5).

 

The code (view source)

  • Start with primes 2 & 3 in hand.
  • Starting at 5, increment by 2, then by 4. Repeat while adding these numbers to the possiblePrimes[] array.
  • Multiply the numbers in the possiblePrimes[] array together. If the multiples exist in rows 1 or 5, add them to the multiples[] array.
  • Compare arrays. Remove numbers from possiblePrimes[] if they also exist in multiples[].