login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A090684 Primes of the form 8n^2 - 1. 11
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 21 16:50 EDT 2019. Contains 328302 sequences. (Running on oeis4.)