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 A249556 #3 Nov 01 2014 14:44:57 %S A249556 1,7,61,433,883,2003,4241,6121,26293,52903 %N A249556 Odd numbers n such that 2n is a term in A247665. %C A249556 It appears that this list only contains 1 and primes. %Y A249556 Cf. A247665. %K A249556 nonn,more %O A249556 1,2 %A A249556 _N. J. A. Sloane_, Nov 01 2014