A119609 p^2-p-1 that is not prime, where p is prime.

1, 155, 341, 505, 1331, 1639, 1805, 2755, 3421, 5255, 6161, 6805, 7831, 10505, 11341, 11771, 12655, 18631, 22649, 24491, 26405, 27721, 29755, 31861, 36289, 37055, 39401, 44309, 49505, 51301, 52211, 54055, 56881, 62749, 65791, 68905, 73169

Offset

1,2

Comments

All prime factors of a(n) {5,11,19,29,31,41,59,61,..} belong to A038872 Primes congruent to {0, 1, 4} mod 5. Also odd primes where 5 is a square mod p. A091568 Primes of the form p^2-p-1, where p is prime. A091567 Primes p such that p^2-p-1 is prime.

Links

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

Mathematica

lst = {}; Do[If[PrimeQ[p] && ! PrimeQ[p^2 - p - 1], AppendTo[lst, p^2 - p -1]], {p, 300}]; lst (* Vincenzo Librandi, Sep 08 2012 *)

Prog

(Magma) [q: p in PrimesUpTo(300) | IsPrime(p) and not IsPrime(q) where q is p^2 - p - 1] // Vincenzo Librandi, Sep 08 2012

Crossrefs

Cf. A091568, A091567, A038872.

Sequence in context: A252805 A089256 A112136 * A063340 A105986 A259957

Adjacent sequences: A119606 A119607 A119608 * A119610 A119611 A119612

Keyword

nonn

Author

Alexander Adamchuk, Jul 27 2006

Status

approved