OFFSET
0,2
COMMENTS
Also the number of ascending runs of length n+10 in the permutations of [2n+10].
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..300
FORMULA
MAPLE
a:= proc(n) option remember; `if`(n<2, 1+21*n, 2*(n+5)*(2*n+9)*
(n^3+22*n^2+132*n+131)*a(n-1)/((n+12)*(n^3+19*n^2+91*n+20)))
end:
seq(a(n), n=0..25);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 16 2013
STATUS
approved