OFFSET
15,3
LINKS
Joerg Arndt and Alois P. Heinz, Table of n, a(n) for n = 15..1000
FORMULA
a(n) ~ c * 2^n, where c = 0.00004645976701216392005148703795279235922588728788878226802174676992574918... . - Vaclav Kotesovec, Sep 07 2014
EXAMPLE
a(17) = 3: 123416, 123452, 1234511.
a(18) = 7: 123156, 123426, 123453, 1234161, 1234512, 1234521, 12345111.
a(19) = 16: 121456, 123256, 123436, 123454, 1231561, 1234117, 1234162, 1234261, 1234513, 1234522, 1234531, 12341611, 12345112, 12345121, 12345211, 123451111.
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, 6))
end:
a:= n-> coeff(b(n, 1), x, 5):
seq(a(n), n=15..50);
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, 6}]]; a[n_] := SeriesCoefficient[b[n, 1], {x, 0, 5}]; Table[a[n], {n, 15, 50}] (* Jean-François Alcover, Nov 07 2014, after Maple *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Joerg Arndt and Alois P. Heinz, Apr 11 2014
STATUS
approved