OFFSET
0,3
FORMULA
a(0) = 1; a(n) = 2^(n-1) * a(n-1) + Sum_{k=0..n-2} a(k) * a(n-k-2).
a(n) ~ c * 2^(n*(n-1)/2), where c = 1.903611332661849505687584024897203124045921097899485586512432930506328189... - Vaclav Kotesovec, Nov 06 2021
MATHEMATICA
nmax = 16; A[_] = 0; Do[A[x_] = (1 + x A[2 x])/(1 - x^2 A[x]) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
a[0] = 1; a[n_] := a[n] = 2^(n - 1) a[n - 1] + Sum[a[k] a[n - k - 2], {k, 0, n - 2}]; Table[a[n], {n, 0, 16}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 05 2021
STATUS
approved