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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. 4
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 (list; graph; refs; listen; history; text; internal format)
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 * A036791 A180136 A010129

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

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Last modified January 27 10:31 EST 2021. Contains 340461 sequences. (Running on oeis4.)