%I #12 Dec 29 2021 04:02:49
%S 1,2,23,480,14627,587580,29331038,1750923328,121673580435,
%T 9648709656300,859874920598850,85078769750118144,9254316901029412110,
%U 1097635452798476278232,140986468651523106196060,19496446561112852736019200,2887977880849714395963280515
%N a(n) = [x^n] Product_{k=1..n} 1/(1 - k*x)^2.
%F a(n) = Sum_{k=0..n} Stirling2(n+k, n) * Stirling2(2*n-k, n).
%F a(n) ~ c * d^n * (n-1)!, where d = 27 / (4*LambertW(-3*exp(-3/2)/2)^2 * (3 + 2*LambertW(-3*exp(-3/2)/2))) = 9.858422414446789720857925020919293523149... and c = 0.28482428628793763109169664913715827647091747... - _Vaclav Kotesovec_, Dec 28 2021
%t a[n_] := Coefficient[Series[Product[1/(1 - k*x)^2, {k, 1, n}], {x, 0, n}], x, n]; Array[a, 17, 0] (* _Amiram Eldar_, Dec 28 2021 *)
%t Table[Sum[StirlingS2[n + k, n]*StirlingS2[2*n - k, n], {k, 0, n}], {n, 0, 20}] (* _Vaclav Kotesovec_, Dec 29 2021 *)
%o (PARI) a(n) = sum(k=0, n, stirling(n+k, n, 2)*stirling(2*n-k, n, 2));
%Y Cf. A007820, A008277, A129256, A298851, A350366.
%K nonn
%O 0,2
%A _Seiichi Manyama_, Dec 27 2021