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 A027208 #17 Oct 25 2019 16:51:53
%S A027208 1,4,19,72,338,1289,6027,23117,107746,415058,1929383,7456777,34584731,
%T A027208 134005510,620344059,2408498148,11131638368,43289074671,199800878749,
%U A027208 778025282080,3586777011141,13982303458588,64394916131100,251261623174835,1156165698462868,4514741175877259
%N A027208 a(n) = Sum_{k=0..n-1} T(n,k) * T(n,k+1), with T given by A026725.
%p A027208 A027208 := proc(n)
%p A027208 add( A026725(n,k)*A026725(n,k+1),k=0..n-1) ;
%p A027208 end proc: # _R. J. Mathar_, Oct 21 2019
%K A027208 nonn
%O A027208 1,2
%A A027208 _Clark Kimberling_
%E A027208 Name corrected by _R. J. Mathar_, Oct 21 2019
%E A027208 More terms from _Sean A. Irvine_, Oct 24 2019