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 A058519 #5 Mar 30 2012 16:48:55
%S A058519 0,1,2,3,5,8,15,24,46,82,157,293,576,1095,2138,4156,8162,16019,31675,
%T A058519 62608,124341,247224,493067,984905,1971970,3953749,7941397,15971775,
%U A058519 32168510,64866564,130959749,264676274,535488128,1084424916
%N A058519 Number of directed cycles of B-trees of order 3 with n labeled leaves.
%p A058519 spec := [C, {B=Union(Z, Subst(M, B)), M=Union(Prod(Z,Z),Prod(Z,Z,Z)), C=Cycle(B)}]; [seq(combstruct[count](spec, size=n), n=0..40)];
%Y A058519 Cf. A058518, A014535.
%K A058519 nonn
%O A058519 0,3
%A A058519 _N. J. A. Sloane_, Dec 21 2000