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 A232445 #20 Sep 26 2014 16:19:06 %S A232445 1,11177320,182937066,159839399818,166474679436 %N A232445 Numbers n such that sigma(n) and sigma(n^2) are squares. %C A232445 Intersection of A006532 and A008847. %C A232445 sigma(a(6)) >= 10^12. - _Hiroaki Yamanouchi_, Sep 26 2014 %e A232445 sigma(a(2)) = (64*9*5*2)^2 and sigma(a(2)^2) = (3*7*13*19*31*127)^2. %e A232445 sigma(a(3)) = (64*9*5*7)^2 and sigma(a(3)^2) = (3*7*13*37*61*499)^2. %e A232445 sigma(a(4)) = (256*9*5*47)^2 and sigma(a(4)^2) = (3*49*13*19*37*43*61*67)^2. %e A232445 sigma(a(5)) = (16*3*7*121*17)^2 and sigma(a(5)^2) = (3*49*13*31*61*109*757)^2. %o A232445 (PARI) isok(n) = issquare(sigma(n)) && issquare(sigma(n^2)); \\ _Michel Marcus_, Sep 24 2014 %Y A232445 Cf. A000203 (sigma: sum of divisors of n), A006532, A008847, A232444. %K A232445 nonn,hard,more %O A232445 1,2 %A A232445 _Alex Ratushnyak_, Nov 24 2013 %E A232445 a(4) from _Hiroaki Yamanouchi_, Sep 24 2014 %E A232445 a(5) from _Hiroaki Yamanouchi_, Sep 26 2014