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 A278883 #9 Dec 02 2016 03:14:35
%S A278883 1,5,81,1872,51425,1565109,50979600,1742711616,61765676577,
%T A278883 2251396558125,83924761860225,3186277484832000,122829049870699536,
%U A278883 4796448751641900752,189381233826675892800,7549371503605704934656,303473219026059360959265,12289574902507266828093525,500960076377670398672062425,20540854991655352005504930000,846696245823312839372671355025,35068049224094584278339245227125,1458752047374053912228252043321600
%N A278883 a(n) = (4*n+1) * ( binomial(3*n,n)/(2*n+1) )^2.
%C A278883 Central terms of triangle A278880; a(n) = A278880(2*n+1, n) for n>=0.
%o A278883 (PARI) {a(n) = (4*n+1) * ( binomial(3*n,n)/(2*n+1) )^2}
%o A278883 for(n=0,20,print1(a(n),", "))
%Y A278883 Cf. A278880.
%K A278883 nonn
%O A278883 0,2
%A A278883 _Paul D. Hanna_, Nov 29 2016