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 A291847 #9 Sep 03 2017 16:58:43
%S A291847 1,4,26,224,2389,30324,446109,7460928,139775763,2899264620,
%T A291847 65954625560,1632654953280,43688087178059,1256602120453484,
%U A291847 38661480001233486,1266934683224418816,44054989554206606603,1620147926716343851500,62826169539072988352134,2562071016044926371845920,109611597248567432265872903,4908887251696851858305862332
%N A291847 A diagonal of irregular triangle A291845.
%C A291847 G.f. of row n in triangle A291845 equals Product_{k=0..n-1} (1 + (2*k+1)*x + x^2), with row sums equal to the odd double factorials A001147.
%H A291847 Paul D. Hanna, <a href="/A291847/b291847.txt">Table of n, a(n) for n = 0..300</a>
%F A291847 a(n) = A291845(n+1,n).
%o A291847 (PARI) /* As a Diagonal in Triangle A291845 */
%o A291847 {A291845(n, k)=polcoeff(prod(j=0, n-1, 1 + (2*j+1)*x + x^2), k)}
%o A291847 {for(n=0,25,print1(A291845(n+1,n),", "))}
%Y A291847 Cf. A291845, A291846, A291848.
%K A291847 nonn
%O A291847 0,2
%A A291847 _Paul D. Hanna_, Sep 03 2017