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 A117187 #9 Jan 30 2020 21:29:15
%S A117187 1,1,4,4,15,15,56,56,210,210,792,792,3003,3003,11440,11440,43758,
%T A117187 43758,167960,167960,646646,646646,2496144,2496144,9657700,9657700,
%U A117187 37442160,37442160,145422675,145422675,565722720
%N A117187 Expansion of (1+x)c(x^2)/((1-x^2*c(x^2))sqrt(1-4x^2)), c(x) the g.f. of A000108.
%C A117187 Diagonal sums of triangle A117184. Also second column of triangle A117184.
%F A117187 E.g.f.: dif(Bessel_I(1,2x)+Bessel_I(2,2x)+Bessel_I(3,2x),x);
%F A117187 a(n)=sum{k=0..n, C(n-k+1,n/2+1)(1+(-1)^n)/2+C(n-k, n/2+1/2)(1-(-1)^n)/2}.
%F A117187 Conjecture D-finite with recurrence: (n+4)*(31n-12)*a(n) +(37n^2+24n-156)*a(n-1) -4*(31n^2+81n+24)*a(n-2) -4*(37n+24)*(n-1)*a(n-3) =0. - _R. J. Mathar_, Dec 10 2011
%K A117187 easy,nonn
%O A117187 0,3
%A A117187 _Paul Barry_, Mar 01 2006