OFFSET
6,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 6..500
EXAMPLE
a(6) = 2: 123546, 123564.
a(7) = 68: 1243756, 1243765, 1247365, ..., 6123574, 7123546, 7123564.
MAPLE
b:= proc(u, o) option remember; `if`(u+o=0, 1, add(
b(u-j, o+j-1), j=1..u)+add(convert(series(
b(u+j-1, o-j)*x^(o-j), x, 9), polynom), j=1..o))
end:
a:= n-> coeff(b(n, 0), x, 8):
seq(a(n), n=6..25);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 14 2015
STATUS
approved