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A258775 Numbers n such that 1 + sigma(n)+ sigma(n)^2 is prime.

%I A258775 #18 Sep 08 2022 08:46:12
%S A258775 1,2,5,6,7,8,11,13,14,15,19,23,34,37,40,45,49,53,57,58,60,61,78,79,89,
%T A258775 92,105,106,109,123,129,132,137,138,140,141,143,148,149,154,155,156,
%U A258775 160,161,163,165,167,182,188,191,193,195,201,208,212,213,222,226
%N A258775 Numbers n such that 1 + sigma(n)+ sigma(n)^2 is prime.
%C A258775 Also numbers n such that A000203(n) is in A002384. - _Robert Israel_, Jun 09 2015
%H A258775 Robert Price, <a href="/A258775/b258775.txt">Table of n, a(n) for n = 1..2122</a>
%H A258775 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 A258775 select(isprime @ (t -> 1+t+t^2) @ numtheory:-sigma, [$1..1000]); # _Robert Israel_, Jun 09 2015
%t A258775 Select[ Range[10000], PrimeQ[ 1 + DivisorSigma[1, #] + DivisorSigma[1, #]^2] & ]
%t A258775 Select[ Range[10000], PrimeQ[ Cyclotomic[3, DivisorSigma[1, #]]] &]
%o A258775 (PARI) for(n=1,10^3,if(isprime(1+sigma(n)+sigma(n)^2),print1(n,", "))) \\ _Derek Orr_, Jun 09 2015
%o A258775 (Magma) [n: n in [1..250] | IsPrime(1 + SumOfDivisors(n)+ SumOfDivisors(n)^2)]; // _Vincenzo Librandi_, Jun 10 2015
%Y A258775 Cf. A002384, A000203, A258774, A258776.
%K A258775 nonn
%O A258775 1,2
%A A258775 _Robert Price_, Jun 09 2015