OFFSET
1,2
LINKS
J.-L. Baril, Classical sequences revisited with permutations avoiding dotted pattern, Electronic Journal of Combinatorics, 18 (2011), #P178. See Table 3.
MAPLE
b:= proc(n) option remember; `if`(n<1, 1, b(n-1)+(n-1)*b(n-2)) end:
a:= proc(n) option remember; `if`(n<2, 0,
b(n)-add(a(r)*b(n-1-r), r=1..n-1))
end:
seq(a(n), n=1..28); # Alois P. Heinz, Apr 14 2022
MATHEMATICA
b[n_] := b[n] = If[n < 1, 1, b[n - 1] + (n - 1)*b[n - 2]];
a[n_] := a[n] = If[n < 2, 0, b[n] - Sum[a[r]*b[n - 1 - r], {r, 1, n - 1}]];
Table[a[n], {n, 1, 28}] (* Jean-François Alcover, Apr 15 2022, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 03 2011
STATUS
approved