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 A248963 #16 Aug 18 2019 04:31:38 %S A248963 1,7,9,11,13,16,19,23,25,29,31,32,37,43,47,53,61,67,73,79,81,83,97, %T A248963 103,107,109,113,121,127,128,137,139,149,151,157,163,179,181,191,193, %U A248963 197,199,211,223,227,229,233,239,241,243,251,257,263,269,271,277,281,283,307,311,313,317,331 %N A248963 Prime powers p^m for which sigma(p^2m) is not prime. %C A248963 sigma(x) cannot be prime unless x is a square of a prime power, x = p^2m, cf. A055638 and A023194. This sequence lists the complement: prime powers whose square does not have a prime sum of divisors. %C A248963 Although generally 1 is not considered a prime power, it seemed logical for various good reasons to include the initial term a(1)=1. %H A248963 Amiram Eldar, <a href="/A248963/b248963.txt">Table of n, a(n) for n = 1..10000</a> %F A248963 A248963 = A000961 \ A055638, i.e., the complement of A055638 in A000961. %o A248963 (PARI) for(n=1,999,isprimepower(n)||next;isprime(sigma(n^2))||print1((n)",")) %Y A248963 Cf. A000961, A055638, A023194, A023195, A062700. %K A248963 nonn %O A248963 1,2 %A A248963 _M. F. Hasler_, Oct 18 2014