OFFSET
6,3
LINKS
Joerg Arndt and Alois P. Heinz, Table of n, a(n) for n = 6..1000
FORMULA
a(n) ~ c * 2^n, where c = 0.01795631780689407343024911217251418606332716557572090051127381129853009022... . - Vaclav Kotesovec, Sep 07 2014
EXAMPLE
a(8) = 3: 1214, 1232, 12311.
a(9) = 7: 1134, 1224, 1233, 12141, 12312, 12321, 123111.
a(10) = 12: 11341, 12115, 12142, 12241, 12313, 12322, 12331, 121411, 123112, 123121, 123211, 1231111.
MAPLE
b:= proc(n, i) option remember; `if`(n=0, 1, series(
add(b(n-j, i+1)*`if`(i=j, x, 1), j=1..n), x, 4))
end:
a:= n-> coeff(b(n, 1), x, 3):
seq(a(n), n=6..45);
MATHEMATICA
b[n_, i_] := b[n, i] = If[n == 0, 1, Series[Sum[b[n-j, i+1]*If[i == j, x, 1], {j, 1, n}], {x, 0, 4}]]; a[n_] := SeriesCoefficient[b[n, 1], {x, 0, 3}]; Table[a[n], {n, 6, 45}] (* Jean-François Alcover, Nov 07 2014, after Maple *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Joerg Arndt and Alois P. Heinz, Apr 11 2014
STATUS
approved