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 A248426 #7 Oct 13 2014 04:07:19 %S A248426 1,3,11,46,211,1038,5400,29425,166767,977637,5901299,36538483, %T A248426 231286924,1492482109,9793849702,65217085321,439887071563, %U A248426 3000650380603,20673092451143,143687057466690,1006538694994567,7100409431126274,50404258628152846,359845398688215262 %N A248426 Number of permutations of length n avoiding the pattern 1342 and with 1 appearing before n. %F A248426 G.f.: (-1 + sqrt((8*x-1)*sqrt(1-8*x) - 136*x^2 + 20*x + 1)/sqrt((8*x-1)*sqrt(1-8*x) - 8*x^2 + 20*x + 1))*((8*x-1)*sqrt(1-8*x) - 8*x^2 - 12*x + 1)/(64*x). %e A248426 For n=4 the 11 permutations are: 1234, 1243, 1324, 1423, 1432, 2134, 2143, 2314, 3124, 3142, 3214. %Y A248426 Cf. A022558. %K A248426 nonn %O A248426 2,2 %A A248426 _Nathaniel Shar_, Oct 06 2014