OFFSET
2,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 2..1665 (terms n=2..59 from R. H. Hardin)
FORMULA
a(n) = Sum_{j=1..n} binomial(n,j)*binomial(n-j,j) = 2*A097861(n).
a(n) = A002426(n) - 1. - Jeppe Stig Nielsen, Dec 13 2019
MAPLE
b:= proc(n, i, k) option remember; `if`(n=0, 1,
`if`(i=0, 0, add(b(n-j, i-1, k), j=0..min(n, k))))
end:
a:= n-> (k-> b(n$2, k)-b(n$2, k-1))(2):
seq(a(n), n=2..30); # Alois P. Heinz, Aug 17 2018
PROG
(PARI) for(n=2, 29, print1(sum(j=1, n, binomial(n, j)*binomial(n-j, j)), ", ")) \\ Hugo Pfoertner, Dec 13 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Aug 24 2010
STATUS
approved