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 A131701 #6 Oct 31 2013 12:17:43 %S A131701 4,6,1,9,7,7,6,8,9,0,3,3,0,3,6,8,9,3,8,0,6,8,2,1,1,9,9,6,8,4,3,7,4,2, %T A131701 3,8,4,0,1,7,2,8,2,5,5,6,4,4,1,2,9,2,3,3,8,9,8,4,2,0,8,2,3,2,9,6,3,7, %U A131701 4,4,6,3,0,8,4,4,2,5,9,6,4,4,8,6,7,2,8,7,1,8,8,0,3,1,6,6,5,0,8,2,3,6,4,2,8 %N A131701 Decimal expansion of the continued fraction 4+6/(9+10/(14+15/21+...)) where the terms are the semiprimes: A001358. %e A131701 4.6197768903303689380682119968437423840172825564412923389842082329... %t A131701 semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; lst = Select[Range@ 400, semiPrimeQ@ # &]; First@ RealDigits@ N[ Fold[ Last@ #2 + First@ #2/#1 &, 4, Partition[Reverse@ lst, 2]], 111] (* _Robert G. Wilson v_ *) %Y A131701 Cf. A001358, A113011. %K A131701 cons,nonn %O A131701 1,1 %A A131701 _Jonathan Vos Post_ & _Robert G. Wilson v_, Sep 08 2007