OFFSET
6,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 6..500
EXAMPLE
a(6) = 11: 345612, 345621, 356241, 456123, 456132, 456213, 456312, 456321, 562341, 563412, 563421.
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^u, x, 7), polynom), j=1..o))
end:
a:= n-> coeff(b(n, 0), x, 6):
seq(a(n), n=6..25);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 14 2015
STATUS
approved