A090684 Primes of the form 8*n^2 - 1.

7, 31, 71, 127, 199, 647, 967, 1151, 1567, 2311, 2591, 2887, 3527, 4231, 4999, 5407, 6271, 7687, 8191, 11551, 12799, 16927, 19207, 20807, 23327, 25087, 27847, 31751, 34847, 35911, 39199, 47431, 49927, 51199, 53791, 59167, 63367, 69191, 70687

Offset

1,1

Comments

In the odd number variant of the Ulam spiral, unimpeded by even numbers, prime numbers can line up in horizontal and vertical lines. But there are still noticeable diagonal lines of primes, and these primes fall on one such diagonal.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..10000

Mathematica

Select[Table[8n^2 - 1, {n, 9000}], PrimeQ] (* Alonso del Arte, Mar 27 2011 *)

Prog

(PARI) mx2pmp(n, m) = { for(x=1, n, y = 8*x^2-1; if(isprime(y), print1(y", ")) ) }
(Magma) [8*n^2-1: n in [1..95] | IsPrime(8*n^2-1)];  // Bruno Berselli, Mar 28 2011

Crossrefs

Sequence in context: A105428 A050547 A157914 * A033199 A304163 A003550

Adjacent sequences: A090681 A090682 A090683 * A090685 A090686 A090687

Keyword

easy,nonn

Author

Cino Hilliard, Dec 18 2003

Status

approved