OFFSET
0,5
FORMULA
a(n) = n! * Sum_{k=0..floor(n/3)} binomial(n-1,n-3*k)/(6^k * k!).
a(0) = 1; a(n) = ((n-1)!/6) * Sum_{k=3..n} (-1)^(k-3) * k * binomial(-3,k-3) * a(n-k)/(n-k)!.
a(n) ~ 2^(-9/8) * exp(-1/24 + 5*2^(1/4)*n^(1/4)/48 - sqrt(2*n)/4 + 2^(7/4)*n^(3/4)/3 - n) * n^(n - 1/8) * (1 - 1203*2^(3/4)/(10240*n^(1/4))). - Vaclav Kotesovec, Mar 29 2023
MATHEMATICA
With[{nn=30}, CoefficientList[Series[Exp[x^3/(6(1-x)^3)], {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, May 20 2023 *)
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(exp(x^3/(6*(1-x)^3))))
(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=(i-1)!/6*sum(j=3, i, (-1)^(j-3)*j*binomial(-3, j-3)*v[i-j+1]/(i-j)!)); v;
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 16 2023
STATUS
approved