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 A352802 #39 Apr 10 2022 01:55:58
%S A352802 1,0,3,3,15,45,198,972,5652,37881,289548,2492640,23906475,253012653,
%T A352802 2930556024,36883817127,501315357690,7318715960511,114224260779891,
%U A352802 1897913866979529,33449523840512127,623265596538965334,12241892922194658510,252793167644378784006
%N A352802 Expansion of Sum_{k>=0} x^k * Product_{j=0..k-1} (j + 3 * x).
%H A352802 Seiichi Manyama, <a href="/A352802/b352802.txt">Table of n, a(n) for n = 0..451</a>
%F A352802 a(n) = Sum_{k=0..floor(n/2)} 3^k * |Stirling1(n-k,k)|.
%t A352802 a[n_] := Sum[3^k * Abs[StirlingS1[n - k, k]], {k, 0, Floor[n/2]}]; Array[a, 25, 0] (* _Amiram Eldar_, Apr 09 2022 *)
%o A352802 (PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=0, N, x^k*prod(j=0, k-1, j+3*x)))
%o A352802 (PARI) a(n) = sum(k=0, n\2, 3^k*abs(stirling(n-k, k, 1)));
%Y A352802 Cf. A343579, A353252, A353253, A353254.
%Y A352802 Cf. A097342.
%K A352802 nonn
%O A352802 0,3
%A A352802 _Seiichi Manyama_, Apr 09 2022