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 A127847 #4 Aug 29 2015 15:29:47
%S A127847 0,1,20,1344,348160,357564416,1465657589760,24017731997138944,
%T A127847 1574098141758535761920,412645105639632468417970176,
%U A127847 432690992231222540584116394393600,1814838857553600260569028862094736359424,30447948962887853884238295543591323273401466880
%N A127847 a(n)=4^C(n,2)*(4^n-1)/3.
%C A127847 -a(n) is the Hankel transform of A127846, the series reversion of x/(1+5x+4x^2). Note that (4^n-1)/3 has g.f. x/(1-5x+4x^2).
%t A127847 Table[4^Binomial[n,2] (4^n-1)/3,{n,0,20}] (* _Harvey P. Dale_, Aug 29 2015 *)
%K A127847 easy,nonn
%O A127847 0,3
%A A127847 _Paul Barry_, Feb 02 2007
%E A127847 More terms from _Harvey P. Dale_, Aug 29 2015