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 A336808 #7 Jan 27 2021 18:43:56
%S A336808 1,6,121,5446,435681,54460126,9802822681,2401691556846,
%T A336808 768541298190721,311259225767242006,155629612883621003001,
%U A336808 94155915794590706815606,67792259372105308907236321,57284459169428986026614691246,56138769986040406306082397421081,63156116234295457094342697098716126
%N A336808 a(n) = (n!)^2 * Sum_{k=0..n} 5^(n-k) / (k!)^2.
%F A336808 Sum_{n>=0} a(n) * x^n / (n!)^2 = BesselI(0,2*sqrt(x)) / (1 - 5*x).
%F A336808 a(0) = 1; a(n) = 5 * n^2 * a(n-1) + 1.
%t A336808 Table[n!^2 Sum[5^(n - k)/k!^2, {k, 0, n}], {n, 0, 15}]
%t A336808 nmax = 15; CoefficientList[Series[BesselI[0, 2 Sqrt[x]]/(1 - 5 x), {x, 0, nmax}], x] Range[0, nmax]!^2
%Y A336808 Cf. A006040, A056546, A336804, A336805, A336807.
%K A336808 nonn
%O A336808 0,2
%A A336808 _Ilya Gutkovskiy_, Jan 27 2021