OFFSET
6,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 6..500
EXAMPLE
a(6) = 5: 123645, 123654, 124356, 124536, 124563.
a(7) = 122: 1253746, 1253764, 1254376, ..., 7124356, 7124536, 7124563.
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, 8), polynom), j=1..o))
end:
a:= n-> coeff(b(n, 0), x, 7):
seq(a(n), n=6..25);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 14 2015
STATUS
approved