4 ms·

> https://user-images.githubusercontent.com/2993947/28248599-d34bd822-6a79-11e7-8c63-4085d08dbfc2.png https://user-images.githubusercontent.com/2993947/28248599

• robinhouston 9y ago
  The numbers in the other columns are multiples of 2 or 3, so you wouldn't expect to see any primes in those columns other than 2 and 3 themselves.
• deleted 9y ago
  [deleted]
• icelancer 9y ago
  https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
• jonreem 9y ago
  In base 12 those are just the columns for 1, 5, 7, and 11, the only numbers between 1 and 12 that aren't divisible by any of 12s factors. If you do this for any base the prime numbers will fall in columns like those. Note that there aren't any prime numbers ending in 2 or 5 in base 10 (except 2 and 5), in base 12 it would be the same for numbers ending in 2, 3, 4, 6, 8, 9 and 10.
• air7 9y ago
  Math? Primes will only appear in columns whose index is coprime with 12. That's because 12n+2 is divisible by 2. 12n+3 by 3, etc for 12n+4, 12n+6, 12n+8, 12n+9, 12n+10. (For n>0. that's why there are primes on the first line)
• MatthewWilkes 9y ago
  The unique prime factorisation of 12. 12 factors into 2, 2 and 3. If a column is index 2n or 3n it will never contain a prime after the first row. The columns that match that here are: 2, 3, 4, 6, 8, 10, 12. The columns that don't are 1, 5, 7, 11 - your four.
• MasterScrat 9y ago
  Not exactly what you are seeing but check this as well: https://en.wikipedia.org/wiki/Ulam_spiral https://en.wikipedia.org/wiki/Ulam_spiral