A258976 Numbers n such that 1 + sigma(n)^2 is prime.

1, 3, 5, 13, 14, 15, 19, 22, 23, 27, 28, 34, 39, 40, 44, 48, 53, 54, 56, 58, 65, 68, 73, 75, 82, 83, 84, 87, 88, 89, 95, 99, 104, 108, 109, 114, 116, 118, 124, 125, 129, 133, 134, 135, 136, 145, 149, 152, 158, 171, 177, 178, 179, 186, 202, 203, 209, 210, 215

Offset: 1

Author

Robert Price, Jun 15 2015

Keywords

• nonn

Links

• Robert Price, Table of n, a(n) for n = 1..1786
• OEIS Wiki, Cyclotomic Polynomials at x=n, n! and sigma(n)

Crossrefs

Cf. A000203, A258974, A258977.

Programs

Magma

[n: n in [1..250] | IsPrime(1 + DivisorSigma(1, n)^2)]; // Vincenzo Librandi, Jun 16 2015

Maple

with(numtheory): A258976:=n->`if`(isprime(1+sigma(n)^2), n, NULL): seq(A258976(n), n=1..500); # Wesley Ivan Hurt, Jul 09 2015

Mathematica

Select[ Range[10000], PrimeQ[ 1 + DivisorSigma[1, #]^2] & ]
Select[ Range[10000], PrimeQ[ Cyclotomic[4, DivisorSigma[1, #]]] &]

PARI

lista(nn) = for (n=1, nn, if (isprime(1+sigma(n)^2), print1(n, ", "))); \\ Michel Marcus, Jun 17 2015