A373759 Expansion of e.g.f. exp(x^4/(24 * (1 - x)^3)).
1, 0, 0, 0, 1, 15, 180, 2100, 25235, 319410, 4299750, 61815600, 950524575, 15633092475, 274749725250, 5151569172750, 102831791687625, 2179782464359500, 48933251188321500, 1160002995644493000, 28956069155772383625, 759014081927743516875
Offset: 0
Keywords
Programs
-
PARI
a(n) = n!*sum(k=0, n\4, binomial(n-k-1, n-4*k)/(24^k*k!));
-
PARI
a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=(i-1)!/24*sum(j=4, i, j*binomial(j-2, j-4)*v[i-j+1]/(i-j)!)); v;
Formula
a(n) = n! * Sum_{k=0..floor(n/4)} binomial(n-k-1,n-4*k)/(24^k * k!).
a(0) = 1; a(n) = ((n-1)!/24) * Sum_{k=4..n} k * binomial(k-2,k-4) * a(n-k)/(n-k)!.