A005511 a(n) = 1 + a(floor(n/2))*a(ceiling(n/2)) for n > 1, a(1) = 4. (Formerly M3536)

4, 17, 69, 290, 1174, 4762, 20011, 84101, 340461, 1378277, 5590589, 22676645, 95292383, 400440122, 1682945112, 7072978202, 28633110562, 115913692522, 469249565698, 1899647488730, 7705380235154, 31254685366922, 126775802093906, 514230228456026, 2160911540495036

Offset

1,1

Comments

All terms are congruent to 4 mod 13.

References

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

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Maple

a:= proc(n) option remember; `if`(n=1, 4,
      1+(t->a(t)*a(n-t))(iquo(n, 2)))
    end:
seq(a(n), n=1..25);  # Alois P. Heinz, Jul 04 2019

Mathematica

a[1]=4; a[n_]:=a[n]=1+a[Floor[n/2]]*a[Ceiling[n/2]]; Table[a[n], {n, 1, 22}] (* Jean-François Alcover, Mar 21 2011 *)

Prog

(PARI) a(n)=if(n<2, if(n<1, 0, 4), 1+a(floor(n/2))*a(ceil(n/2))) /* Ralf Stephan */

Crossrefs

Sequence in context: A033122 A330246 A339065 * A349695 A003127 A172447

Adjacent sequences: A005508 A005509 A005510 * A005512 A005513 A005514

Keyword

nonn,nice

Author

Colin Mallows

Extensions

More terms from Ralf Stephan, Jan 10 2004

Status

approved