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 A273939 #68 Sep 23 2016 06:06:15 %S A273939 1,2,3,5,13,18,67,85,407,492,2867,3359,23021,26380,207681,234061, %T A273939 2080169,2314230,22908239,25222469,275132929,300355398,3579042307, %U A273939 3879397705,50131814767,54011212472,752277576903,806288789375,12040320628153 %N A273939 a(0) = 1, a(1) = 2; for k>0, a(2*k) = k*a(2*k-1) + a(2*k-2), a(2*k+1) = a(2*k) + a(2*k-1). %H A273939 Seiichi Manyama, <a href="/A273939/b273939.txt">Table of n, a(n) for n = 0..896</a> %F A273939 a(n) = A056921(n) + A056922(n). %Y A273939 Cf. A056921, A056922, A058798. %K A273939 nonn %O A273939 0,2 %A A273939 _Seiichi Manyama_, Sep 22 2016