A165354 Primes p such that p+(p^2-1)/8 is integer but not a prime number.

3, 5, 11, 13, 19, 29, 37, 43, 47, 53, 59, 61, 67, 83, 89, 97, 101, 107, 109, 131, 137, 139, 149, 157, 163, 167, 173, 179, 181, 193, 197, 199, 211, 223, 227, 229, 239, 241, 251, 263, 269, 271, 277, 283, 293, 307, 313, 317, 331, 347, 349, 353, 359, 373, 379, 389

Offset

1,1

Comments

For p=2, p+(p^2-1)/8 is not integer; for all others, p=4k+-1, it is integer.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Formula

A000040 \ {{2} U A165353}. - R. J. Mathar, Sep 21 2009

Mathematica

Select[Prime[Range[2, 500]], ! PrimeQ[(#^2 - 1) / 8 + #]&] (* Vincenzo Librandi, Sep 12 2013 *)

Prog

(Magma) [p: p in PrimesUpTo(500)| not IsPrime(Floor(p+(p^2-1)/8))]; // Vincenzo Librandi, Sep 12 2013

Crossrefs

Cf. A165352, A165353.

Sequence in context: A059639 A059263 A066652 * A059638 A059265 A059314

Adjacent sequences: A165351 A165352 A165353 * A165355 A165356 A165357

Keyword

nonn,easy

Author

Vincenzo Librandi, Sep 16 2009

Extensions

Entries checked - R. J. Mathar, Sep 21 2009

Status

approved