A161491 - OEIS

A161491

a(n) = number of primes p less than A000040(n) (the n-th prime) such that (p + 1)*(A000040(n) - 1) is a square

0, 0, 1, 1, 0, 2, 1, 2, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 4, 0, 0, 0, 3, 1, 1, 0, 4, 0, 1, 0, 0, 1, 0, 4, 0, 6, 0, 0, 0, 3, 0, 5, 1, 1, 0, 0, 0, 1, 0, 0, 2, 1, 1, 0, 0, 2, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 2, 0, 0, 1, 1, 1, 0, 1, 0, 6, 0, 0, 1, 1, 0, 1, 0, 0, 6, 2, 0, 0, 0, 0, 1, 2, 0, 0, 0, 0, 1

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OFFSET

1,6

LINKS

Table of n, a(n) for n=1..105.

PROG

(PARI) forprime(q=1, 1000, my(q1=q-1, c=0); forprime(p=1, q-1, issquare((p+1)*q1)&c++); print1(c", ")) \\ M. F. Hasler

CROSSREFS

Sequence in context: A035186 A035194 A245818 * A332998 A301652 A030203

Adjacent sequences: A161488 A161489 A161490 * A161492 A161493 A161494

KEYWORD

nonn

AUTHOR

Creighton Dement, Jun 11 2009

STATUS

approved