OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..800
T. Amdeberhan, V. H. Moll, Involutions and their progenies, 2014
FORMULA
a(n) = Sum_{k=0..n} A000085(k). - Emanuele Munarini, Aug 31 2017
a(n) ~ exp(sqrt(n) - n/2 - 1/4) * n^(n/2) / sqrt(2). - Vaclav Kotesovec, Jun 12 2018
MAPLE
a:= proc(n) option remember; 2*a(n-1)+(n-2)*a(n-2)-(n-1)*a(n-3) end:
a(0), a(1), a(2):= 1, 2, 4:
seq(a(n), n=0..30); # Alois P. Heinz, Oct 19 2014
MATHEMATICA
a[n_] := Sum[StirlingS1[j, k]*2^k*BellB[k, 1/2], {j, 0, n}, {k, 0, j}];
Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Jun 12 2018, after Emanuele Munarini *)
PROG
(Magma) I:=[1, 2, 4]; [n le 3 select I[n] else 2*Self(n-1)-2*Self(n-2)+Self(n-3)+(n-1)*(Self(n-2)-Self(n-3)): n in [1..30]]; // Vincenzo Librandi, Jul 22 2014 // Uses incorrect offset
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 19 2014
EXTENSIONS
More terms from Vincenzo Librandi, Jul 22 2014
STATUS
approved