A258976 - OEIS

%I #18 Sep 08 2022 08:46:13

%S 1,3,5,13,14,15,19,22,23,27,28,34,39,40,44,48,53,54,56,58,65,68,73,75,

%T 82,83,84,87,88,89,95,99,104,108,109,114,116,118,124,125,129,133,134,

%U 135,136,145,149,152,158,171,177,178,179,186,202,203,209,210,215

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

%H Robert Price, <a href="/A258976/b258976.txt">Table of n, a(n) for n = 1..1786</a>

%H OEIS Wiki, <a href="https://oeis.org/wiki/Cyclotomic Polynomials at x=n, n! and sigma(n)">Cyclotomic Polynomials at x=n, n! and sigma(n)</a>

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

%t Select[ Range[10000], PrimeQ[ 1 + DivisorSigma[1, #]^2] & ]

%t Select[ Range[10000], PrimeQ[ Cyclotomic[4, DivisorSigma[1, #]]] &]

%o (Magma) [n: n in [1..250] | IsPrime(1 + DivisorSigma(1, n)^2)]; // _Vincenzo Librandi_, Jun 16 2015

%o (PARI) lista(nn) = for (n=1, nn, if (isprime(1+sigma(n)^2), print1(n, ", "))); \\ _Michel Marcus_, Jun 17 2015

%Y Cf. A000203, A258974, A258977.

%K nonn

%O 1,2

%A _Robert Price_, Jun 15 2015