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 A163162 #18 Mar 10 2022 07:53:36 %S A163162 1,3,5,6,7,8,10,11,12,13,14,15,17,18,19,20,21,22,23,24,26,27,28,29,30, %T A163162 31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53, %U A163162 54,55,56,57,58,59,60,61,62,63,65,66,67,68,69,70,71,72,73,74,75,76,77 %N A163162 Numbers k such that sigma(k) is not prime. %H A163162 Vincenzo Librandi, <a href="/A163162/b163162.txt">Table of n, a(n) for n = 1..1000</a> %F A163162 A000027 \ A023194. %F A163162 a(n) ~ n. - _Charles R Greathouse IV_, May 27 2011 %e A163162 a(1)=1 because A000203(1) is not prime. a(2)=3 because A000203(3)=3 is not prime. a(3)=5 because sigma(5)=6 is not prime. %t A163162 Select[Range[1000], ! PrimeQ[DivisorSigma[1, #]]&] (* _Vincenzo Librandi_, Jan 18 2013 *) %o A163162 (Magma) [n: n in [1..80]| not IsPrime(SumOfDivisors(n))]; // _Vincenzo Librandi_, Jan 18 2013 %o A163162 (PARI) isok(k) = !isprime(sigma(k)); \\ _Michel Marcus_, Mar 10 2022 %Y A163162 Complement of A023194. %Y A163162 Cf. A000203. %K A163162 nonn,easy %O A163162 1,2 %A A163162 _Juri-Stepan Gerasimov_, Jul 22 2009 %E A163162 Edited by _R. J. Mathar_, Jul 25 2009