OFFSET
0,2
COMMENTS
Exponential self-convolution of A007838.
FORMULA
a(n) ~ exp(-2*gamma) * n! * n, where gamma is the Euler-Mascheroni constant A001620. - Vaclav Kotesovec, Mar 24 2024
MATHEMATICA
nmax = 21; CoefficientList[Series[Product[(1 + x^k/k)^2, {k, 1, nmax}], {x, 0, nmax}], x] Range[0, nmax]!
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Mar 24 2024
STATUS
approved