A240801 Triangle read by rows: T(n,k) (n>=2, 0 <= k <= n-2) = number of possible topologies with n given vertices and n-k-2 Steiner points.

1, 1, 3, 3, 12, 12, 15, 75, 120, 60, 105, 630, 1350, 1200, 360, 945, 6615, 17640, 22050, 12600, 2520

Offset

2,3

Links

Table of n, a(n) for n=2..22.

E. N. Gilbert and H. O. Pollak, Steiner minimal trees, SIAM J. Appl. Math. 16, (1968), pp. 1-29. See Table 1.

Example

Triangle begins:
1
1,3
3,12,12
15,75,120,60
105,630,1350,1200,360
945,6615,17640,22050,12600,2520
...

Crossrefs

Row sums = A104653. A001710 and A001147 are diagonals.

Sequence in context: A065957 A303309 A268774 * A032308 A117856 A074850

Adjacent sequences: A240798 A240799 A240800 * A240802 A240803 A240804

Keyword

nonn,tabl,more

Author

N. J. A. Sloane, Apr 13 2014

Status

approved