OFFSET
6,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 6..500
EXAMPLE
a(6) = 1: 123456.
a(7) = 28: 1236475, 1236547, 1236574, 1236745, 1236754, 1237456, 1243576, 1245376, 1245736, 1245763, 1246357, 1253467, 1324567, 1342567, 1345267, 1345627, 1345672, 2134567, 2314567, 2341567, 2345167, 2345617, 2345671, 3124567, 4123567, 5123467, 6123457, 7123456.
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, 11), polynom), j=1..o))
end:
a:= n-> coeff(b(n, 0), x, 10):
seq(a(n), n=6..25);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 14 2015
STATUS
approved