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A359249
a(n) is the number of primes p such that (n/p)^2 + 1 is prime.
0
0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 2, 1, 1, 0, 0, 1, 1, 1, 2, 0, 1, 1, 0, 0, 1, 0, 2, 1, 2, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 2, 1, 1, 0, 1, 1, 2, 0, 1, 0, 2, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 2, 1, 2, 1, 1, 0, 1, 0, 2, 1, 2, 0, 1, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1
OFFSET
1,12
EXAMPLE
a(12) = 2 because 12 = 2*6 (p = 2 and q = 6^2 + 1 = 37) and 12 = 3*4 (p = 3 and q = 4^2 + 1 = 17).
PROG
(Magma) [#[p: p in [1..n] | n mod p eq 0 and IsPrime(p) and IsPrime((n^2 div p^2) + 1)]: n in [1..100]];
(PARI) a(n) = sumdiv(n, p, isprime(p) && isprime((n/p)^2+1)); \\ Michel Marcus, Dec 23 2022
CROSSREFS
Sequence in context: A016388 A016004 A327802 * A284996 A215029 A362832
KEYWORD
nonn
AUTHOR
STATUS
approved