OFFSET
1,3
COMMENTS
a(n) = A158621(n-1) for n > 2. - Georg Fischer, Oct 23 2018
FORMULA
Product_{i=2..n-1} (i^3 + 1), for n>2.
a(n) ~ cosh(sqrt(3)*Pi/2) / (2*Pi) * ((n-1)!)^3.
a(n) = A255433(n-1)/2.
MATHEMATICA
Clear[a]; a[1]=1; a[n_]:= a[n] = Sum[i^3*a[i], {i, 1, n-1}]; Table[a[n], {n, 1, 20}]
Flatten[{1, Table[FullSimplify[Cosh[Sqrt[3]*Pi/2] * Gamma[n+1] * Gamma[n-1/2 - I*Sqrt[3]/2] * Gamma[n-1/2 + I*Sqrt[3]/2] / (2*Pi)], {n, 2, 20}]}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Mar 13 2015
STATUS
approved