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 A188476 #9 Aug 27 2025 14:39:07
%S A188476 1,1,2,6,12,27,65,150,353,843,2014,4843,11713,28433,69292,169470,
%T A188476 415754,1022868,2523120,6238645,15459561,38387191,95497612,237989801,
%U A188476 594062697,1485141397,3718116380,9320941698,23396109986,58795356627,147920737819
%N A188476 Diagonal sums of number triangle A188474.
%C A188476 Hankel transform is A188477(n+1).
%F A188476 a(n)=sum{k=0..floor(n/2), sum{j=0..n-2k+1, (j/(n-k+2-j))*C(n-k+2-j,n-k+1)*C(n-k+2-j,k+1)*2^(j-1)}}.
%F A188476 Conjecture: (n+3)*a(n) +(-4*n-9)*a(n-1) +n*a(n-2) -3*a(n-3) +3*(5*n+1)*a(n-4) +6*(n)*a(n-5) +6*(n-1)*a(n-6) +4*(-n+3)*a(n-7)=0. - _R. J. Mathar_, Dec 03 2014
%K A188476 nonn,easy,changed
%O A188476 0,3
%A A188476 _Paul Barry_, Apr 01 2011