OFFSET
0,4
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..576
Wikipedia, Partition of a set
EXAMPLE
a(4) = 7: 4321, 43|21, 43|2|1, 421|3, 4|321, 4|32|1, 41|3|2.
MAPLE
b:= proc(n, m) option remember; series(`if`(n=0, 1, add(
`if`(j=n, x, 1)*b(n-1, max(m, j)), j=1..m+1)), x, 2)
end:
a:= n-> coeff(b(n, 0), x, 1):
seq(a(n), n=0..25);
MATHEMATICA
b[n_, m_] := b[n, m] = Series[If[n == 0, 1, Sum[
If[j == n, x, 1]*b[n-1, Max[m, j]], {j, 1, m+1}]], {x, 0, 2}];
a[n_] := Coefficient[b[n, 0], x, 1];
Table[a[n], {n, 0, 25}] (* Jean-François Alcover, May 16 2022, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jan 09 2022
STATUS
approved