OFFSET
1,2
MATHEMATICA
A[m_, n_] := A[m, n] = Which[m == 1, (2 n - 1)!!, m > n >= 1, 0, True, A[m - 1, n] - A[m - 1, m - 1] A[m, n - m + 1]]; a[n_] := A[n, n]; a /@ Range[1, 20]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, May 23 2023
STATUS
approved