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 A283486 #15 Feb 22 2020 20:54:24 %S A283486 0,1,1,1,0,2,1,0,2,1,0,3,0,1,1,2,0,1,1,1,3,1,0,3,0,0,2,2,0,3,1,0,0,1, %T A283486 0,5,1,0,1,2,0,3,0,0,3,0,0,4,2,0,1,2,0,2,1,1,2,0,0,4,0,2,2,2,0,2,0,0, %U A283486 1,2,0,5,0,0,1,2,0,2,1,1,1,1,0,6,0,0,1,1,0,4,2,0,2,0,0,5 %N A283486 Number of k such that sigma(k) = 2n where sigma(m) = A000203(m) is the sum of the divisors of m. %C A283486 First occurrence of k: 1, 2, 6, 12, 48, 36, 84, ... %H A283486 Charles R Greathouse IV, <a href="/A283486/b283486.txt">Table of n, a(n) for n = 1..10000</a> %F A283486 a(n) = A054973(2n) - _Michel Marcus_, Mar 08 2017. %e A283486 a(12) = 3 because sigma(14) = 1 + 2 + 7 + 14 = 24, sigma(15) = 1 + 3 + 5 + 15 = 24 and sigma(23) = 1 + 23 = 24. %o A283486 (PARI) first(n)=my(v=vector(n),t);for(k=1,2*n-1, t=sigma(k)/2; if(t<=n && denominator(t)==1, v[t]++)); v \\ _Charles R Greathouse IV_, Mar 08 2017 %Y A283486 Cf. A000203, A054973, A060658. %K A283486 nonn %O A283486 1,6 %A A283486 _Juri-Stepan Gerasimov_, Mar 08 2017 %E A283486 a(96) corrected by _Charles R Greathouse IV_, Mar 08 2017