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 A305472 #12 Jun 03 2018 03:46:25
%S A305472 1,3,16,138,1624,24084,430264,8987376,214836496,5782610640,
%T A305472 173048646208,5699040103584,204819346436608,7976556430820544,
%U A305472 334605731401589632,15041304800209892352,721313418947271653632,36756901756710434550528
%N A305472 a(0) = 1, a(1) = 3, a(n) = 3*n*a(n-1) - 2*a(n-2).
%C A305472 Let S(i,j,n) denote a sequence of the form a(0) = 1, a(1) = i, a(n) = i*n*a(n-1) + j*a(n-2). Then S(i,j,n) = Sum_{k=0..floor(n/2)} ((n-k)!/k!)*binomial(n-k,k)*i^(n-2*k)*j^k.
%H A305472 Seiichi Manyama, <a href="/A305472/b305472.txt">Table of n, a(n) for n = 0..380</a>
%F A305472 a(n) ~ BesselJ(0, 2*sqrt(2)/3) * n! * 3^n. - _Vaclav Kotesovec_, Jun 03 2018
%o A305472 (PARI) {a(n) = sum(k=0, n/2, ((n-k)!/k!)*binomial(n-k, k)*3^(n-2*k)*(-2)^k)}
%Y A305472 Cf. A305460, A305471.
%K A305472 nonn
%O A305472 0,2
%A A305472 _Seiichi Manyama_, Jun 02 2018