OFFSET
0,3
FORMULA
a(n) ~ 2^(2*n - 1/2) * n^(n - 1/2) / (sqrt(Pi*(1+c)) * exp(n + (2+c)^2/8) * (c*(2+c))^n), where c = LambertW(2*exp(-2)) = 0.21771510575709011079475830443...
MATHEMATICA
Table[Sum[Binomial[n, k]*Binomial[k^2, n], {k, 0, n}], {n, 0, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Jul 09 2021
STATUS
approved