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 A138462 #15 Mar 25 2024 09:04:34
%S A138462 1,6,90,1806,41586,1037718,27297738,745387038,20927156706,
%T A138462 600318853926,17518619320890,518431875418926,15521467648875090,
%U A138462 469286147871837366,14308406109097843626,439442782615614361662,13582285614213903189954,422158527806921249683014
%N A138462 A bisection of A006318.
%H A138462 Colin Barker, <a href="/A138462/b138462.txt">Table of n, a(n) for n = 0..300</a>
%F A138462 a(n) = A006318(2n).
%F A138462 a(n) = Sum_{i=0..2n} (C(2*n+1,i+1)*C(2*n+i,i))/(2*n+1). - _Vladimir Kruchinin_, Apr 02 2017
%F A138462 D-finite with recurrence +n*(2*n+1)*a(n) +(-70*n^2+73*n-15)*a(n-1) +(70*n^2-277*n+270)*a(n-2) -(2*n-5)*(n-3)*a(n-3)=0. - _R. J. Mathar_, Mar 25 2024
%o A138462 (Maxima)
%o A138462 a(n):=sum(binomial(2*n+1,i+1)*binomial(2*n+i,i),i,0,2*n)/(2*n+1); /* _Vladimir Kruchinin_, Apr 02 2017 */
%o A138462 (PARI) a(n) = sum(i=0, 2*n, binomial(2*n+1,i+1)*binomial(2*n+i,i))/(2*n+1) \\ _Colin Barker_, Dec 28 2017
%K A138462 nonn,easy
%O A138462 0,2
%A A138462 _N. J. A. Sloane_, May 08 2008