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 A259185 #18 Sep 08 2022 08:46:13 %S A259185 2,3,4,5,8,9,10,12,17,18,20,24,26,30,32,36,38,40,41,45,46,51,54,55,56, %T A259185 58,59,60,66,70,71,72,78,86,87,89,91,92,94,95,99,101,102,104,106,108, %U A259185 110,115,116,119,123,125,131,134,138,142,143,144,154,159,164 %N A259185 Numbers n such that 1 - sigma(n) + sigma(n)^2 is prime. %H A259185 Robert Price, <a href="/A259185/b259185.txt">Table of n, a(n) for n = 1..1737</a> %H A259185 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 A259185 with(numtheory): A259185:=n->`if`(isprime(1 - sigma(n) + sigma(n)^2), n, NULL): seq(A259185(n), n=1..500); # _Wesley Ivan Hurt_, Jul 09 2015 %t A259185 Select[ Range[10000], PrimeQ[ 1 - DivisorSigma[1, n] + DivisorSigma[1, n]^2] & ] %t A259185 Select[ Range[10000], PrimeQ[ Cyclotomic[6, DivisorSigma[1, #]]] &] %o A259185 (Magma) [n: n in [1..180] | IsPrime(1 - SumOfDivisors(n) + SumOfDivisors(n)^2)]; // _Vincenzo Librandi_, Nov 20 2015 %o A259185 (PARI) is(n)=my(s=sigma(n)); isprime(s^2-s+1) \\ _Charles R Greathouse IV_, May 22 2017 %Y A259185 Cf. A000203, A259184, A259186. %K A259185 nonn,easy %O A259185 1,1 %A A259185 _Robert Price_, Jun 20 2015