A276476 - OEIS

A276476

a(n) is the number of distinct integers of the form x^2-x-prime(n) for 0<=x<=prime(n)+1 whose absolute value is prime.

1, 2, 3, 5, 6, 9, 9, 13, 11, 17, 20, 17, 10, 32, 16, 23, 26, 30, 25, 21, 55, 38, 30, 27, 25, 34, 57, 19, 83, 49, 44, 40, 39, 60, 37, 77, 54, 57, 27, 43, 79, 67, 45, 110, 42, 93, 79, 79, 43, 85, 46, 90, 96, 41, 54, 96, 127, 107, 63, 78, 181, 67, 78, 72, 189, 51, 77, 103

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..68.

EXAMPLE

a(2)=2 because prime(2)=3 and x^2 - x - 3 generates {-3, -3, -1, 3, 9}. This contains two integers, -3 and 3, whose absolute value is prime.

a(14)=32 because prime(14)=43 and x^2 - x - 43 generates 32 prime numbers for x = 0..44.

PROG

(PARI) isaprime(x) = isprime(x) || isprime(-x);

nbp(n) = {v = vector(prime(n)+2, x, x--; x^2-x-prime(n)); vp = select(x->isaprime(x), v); vp = Set(vp); #vp; } \\ Michel Marcus, Sep 13 2016

CROSSREFS