A256503 Smallest k>=1 such that n^2 + (n+1)^2 + ... + (n+k)^2 is prime or a(n)=0 if there is no such k.

1, 1, 5, 1, 1, 2, 1, 0, 1, 0, 0, 1, 5, 1, 0, 0, 1, 5, 1, 0, 5, 1, 5, 1, 1, 0, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 5, 1, 0, 0, 1, 0, 0, 0, 0, 1, 5, 0, 1, 5, 2, 0, 0, 0, 2, 0, 0, 0, 1, 0, 2, 5, 0, 1, 2, 0, 0, 1, 1, 0, 1, 0, 0, 0, 2, 0, 0, 1, 0, 5, 1, 0, 1, 1, 2, 1

Offset

1,3

Comments

Every term is either 0 or 1 or 2 or 5.

a(n)=0 if and only if n is in A256385.

Links

Table of n, a(n) for n=1..87.

Formula

1) if 2n^2+2n+1 is prime, then a(n)=1;

2) if 2n^2+2n+1 is not prime, but 3n^2+6n+5 is prime, then a(n)=2;

3) if 2n^2+2n+1 and 3n^2+6n+5 are both composite numbers, but 6n^2+30n+55 is prime, then a(n)=5;

4) otherwise, a(n)=0.

Crossrefs

Cf. A000290, A256385, A089306.

Sequence in context: A130511 A320410 A011396 * A379483 A379581 A036791

Adjacent sequences: A256500 A256501 A256502 * A256504 A256505 A256506

Keyword

nonn

Author

Vladimir Shevelev, Mar 31 2015

Extensions

More terms from Peter J. C. Moses, Mar 31 2015

Status

approved