A005469 a(n) = 1 + a(floor(n/2))*a(ceiling(n/2)) for n > 1, a(1) = 2.

2, 5, 11, 26, 56, 122, 287, 677, 1457, 3137, 6833, 14885, 35015, 82370, 194300, 458330, 986390, 2122850, 4570610, 9840770, 21435122, 46689890, 101709206, 221563226, 521198276, 1226050226, 2884185551, 6784816901, 16004491001, 37752490001, 89053519001

Offset: 1

Author

Colin Mallows

Keywords

• nonn

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A005468.

Programs

Maple

a:= proc(n) option remember; `if`(n=1, 2,
      1+(t->a(t)*a(n-t))(iquo(n, 2)))
    end:
seq(a(n), n=1..35);  # Alois P. Heinz, Jul 04 2019

Mathematica

a[n_] := a[n] = If[n==1, 2, 1 + a[Floor[n/2]] a[Ceiling[n/2]]];
a /@ Range[35] (* Jean-François Alcover, Nov 16 2020 *)