This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A258976 #18 Sep 08 2022 08:46:13 %S A258976 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 A258976 82,83,84,87,88,89,95,99,104,108,109,114,116,118,124,125,129,133,134, %U A258976 135,136,145,149,152,158,171,177,178,179,186,202,203,209,210,215 %N A258976 Numbers n such that 1 + sigma(n)^2 is prime. %H A258976 Robert Price, <a href="/A258976/b258976.txt">Table of n, a(n) for n = 1..1786</a> %H A258976 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 A258976 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 A258976 Select[ Range[10000], PrimeQ[ 1 + DivisorSigma[1, #]^2] & ] %t A258976 Select[ Range[10000], PrimeQ[ Cyclotomic[4, DivisorSigma[1, #]]] &] %o A258976 (Magma) [n: n in [1..250] | IsPrime(1 + DivisorSigma(1, n)^2)]; // _Vincenzo Librandi_, Jun 16 2015 %o A258976 (PARI) lista(nn) = for (n=1, nn, if (isprime(1+sigma(n)^2), print1(n, ", "))); \\ _Michel Marcus_, Jun 17 2015 %Y A258976 Cf. A000203, A258974, A258977. %K A258976 nonn %O A258976 1,2 %A A258976 _Robert Price_, Jun 15 2015