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 A056921 #14 Jul 02 2025 16:02:00 %S A056921 0,1,1,2,5,7,26,33,158,191,1113,1304,8937,10241,80624,90865,807544, %T A056921 898409,8893225,9791634,106809565,116601199,1389422754,1506023953, %U A056921 19461710190,20967734143,292042254049,313009988192,4674182088737 %N A056921 a(0) = 0, a(1) = 1, a(2*n) = n*a(2*n-1) + a(2*n-2), a(2*n+1) = a(2*n) + a(2*n-1). %H A056921 Seiichi Manyama, <a href="/A056921/b056921.txt">Table of n, a(n) for n = 0..897</a> %F A056921 Numerators of continued fraction for alternating factorial. %Y A056921 Cf. A058797. %K A056921 frac,easy,nonn %O A056921 0,4 %A A056921 _Aleksandar Petojevic_, Sep 05 2000 %E A056921 More terms from _James Sellers_, Sep 07 2000