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 A173013 #4 Feb 14 2013 17:49:42 %S A173013 1,3,5,7,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2, %T A173013 0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2,0,2 %N A173013 a(1) = 1, for n >= 2; a(n) = the smallest number h such that sigma(h) = A000203(h) = a(n-1) + 3, a(n) = 0 if no such number exists. %C A173013 a(n) is eventually periodic sequence with period (0, 2). %F A173013 A000203(a(n)) = a(n-1) + 3 for n >= 2. %o A173013 (PARI) a(n)=if(n>4,2-n%2*2,2*n-1) \\ _Charles R Greathouse IV_, Feb 14 2013 %Y A173013 Cf. A000035, A173012, A173014, A173015, A173016. %K A173013 nonn,easy %O A173013 1,2 %A A173013 _Jaroslav Krizek_, Nov 06 2010