A047187 Number of nonempty subsets of {1,2,...,n} in which exactly 1/5 of the elements are <= (n-2)/2.

0, 0, 0, 0, 1, 2, 10, 15, 45, 60, 140, 175, 360, 435, 891, 1071, 2415, 2940, 7260, 8910, 22359, 27345, 66625, 80795, 191191, 230230, 541190, 649805, 1548755, 1860131, 4514979, 5426995, 13295955, 15974220, 39112716, 46915104, 114411173

Offset

1,6

Links

Table of n, a(n) for n=1..37.

Prog

(PARI) { a(n) = sum(i=1, n\5, binomial(n\2-1, i) * binomial(n+1-n\2, 4*i) ) } \\ Max Alekseyev, Feb 09 2010

Crossrefs

Sequence in context: A063610 A369650 A181474 * A048043 A370115 A043429

Adjacent sequences: A047184 A047185 A047186 * A047188 A047189 A047190

Keyword

nonn

Author

Clark Kimberling

Extensions

More terms from Max Alekseyev, Feb 09 2010

Status

approved