A212553 Irreducible near matchings over 2n+1 vertices.

3, 15, 126, 1395, 18678, 289926, 5090220, 99466371, 2138575590, 50153137650, 1274013771300, 34853264146350, 1021795130252988, 31964591332833900, 1062945070050997656, 37447053359058465507, 1393372283171378001030

Offset

1,1

Links

Table of n, a(n) for n=1..17.

Takahisa Toda and Ivo Vigan, On Separating Convex Points with Lines

Formula

a(n) = A000699(n+1)*(2*n+1)*(n+1)/(2*n).

Example

a(1) corresponds to the 3-vertex graphs with edge sets {{1,2},{2,3}}, {{1,2},{1,3}} and {{1,3},{2,3}} respectively.
a(2) corresponds to the 5-vertex graphs with edge sets {{1,2},{2,4},{3,5}}, {{1,4},{2,3},{2,5}} ...

Prog

(PARI)
A000699(n)={my(A); A=O(x); for(i=1, n, A=x+A*(2*x*A'-A)); polcoeff(A, n)}
a(n)=A000699(n+1)*(2*n+1)*(n+1)/(2*n);
vector(66, n, a(n))
/* Joerg Arndt, May 27 2012 */

Crossrefs

Cf. A000699, A200142.

Sequence in context: A230657 A246573 A270503 * A229673 A266091 A135255

Adjacent sequences: A212550 A212551 A212552 * A212554 A212555 A212556

Keyword

nonn

Author

Ivo Vigan, May 20 2012

Status

approved