A188225 Number of ways to select 15 knights from n knights sitting at a round table if no adjacent knights are chosen.

2, 31, 256, 1496, 6936, 27132, 93024, 286824, 810084, 2124694, 5230016, 12183560, 27041560, 57500460, 117675360, 232676280, 445962870, 830905245, 1508593920, 2674776720, 4639918800, 7887861960, 13160496960, 21578373360, 34810394760

Offset

30,1

Links

Table of n, a(n) for n=30..54.

Formula

a(n) = C(n - 15, 15) + C(n - 16, 14)

Example

For n = 30 a(30) = C(15, 15) + C(14, 14) = 2

Mathematica

Table[Binomial[n-15, 15]+Binomial[n-16, 14], {n, 30, 60}] (* Harvey P. Dale, May 16 2018 *)

Crossrefs

a(n) = A010968(n - 15) + A010967(n - 16)

Sequence in context: A137626 A134179 A223145 * A164676 A004307 A268879

Adjacent sequences: A188222 A188223 A188224 * A188226 A188227 A188228

Keyword

nonn

Author

Zoltán Lőrincz, Mar 30 2011

Status

approved