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 A173012 #4 Feb 14 2013 17:48:05 %S A173012 1,2,3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, %T A173012 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 %N A173012 a(1) = 1, for n >= 2; a(n) = the smallest number h such that sigma(h) = A000203(h) = a(n-1) + 2, a(n) = 0 if no such number exists. %C A173012 a(1) = 1, a(2) = 2, a(3) = 3, a(n) = 0 for n >= 4. %F A173012 A000203(a(n)) = a(n-1) + 2 for n >= 2. %o A173012 (PARI) a(n)=if(n>3,0,n) \\ _Charles R Greathouse IV_, Feb 14 2013 %Y A173012 Cf. A000035, A173013, A173014, A173015, A173016. %K A173012 nonn,easy %O A173012 1,2 %A A173012 _Jaroslav Krizek_, Nov 06 2010