A204329 Irregular triangle read by rows: T(n,k) (n >= 2) is the number of cubic graphs on 2*n nodes with diameter k.

1, 0, 2, 0, 2, 3, 0, 1, 15, 2, 1, 0, 0, 34, 43, 6, 2, 0, 0, 34, 351, 93, 24, 6, 1, 0, 0, 14, 2167, 1499, 261, 101, 14, 4, 0, 0, 1, 12301, 22992, 4400, 1229, 310, 55, 12, 1, 0, 0, 1, 57628, 338356, 90870, 17281, 5145, 948, 220, 36, 4, 0, 0, 0, 185836, 4692045, 2013271, 321788, 84159, 17894, 3516, 799, 118, 20, 1

Offset: 2

Author

N. J. A. Sloane, Jan 14 2012

Keywords

• nonn
• tabf

Comments

The number of terms in each row (the maximal diameter) begins 1,2,3,5,6,8,... . I don't know how this sequence continues.

The maximal diameter is now provided in A294732, taken from Gordon Royle's Cubic Graphs page. - Hugo Pfoertner, Dec 13 2017

Examples

			Triangle begins:
1
0 2
0 2 3
0 1 15 2 1
0 0 34 43 6 2
0 0 34 351 93 24 6 1
0 0 14 2167 1499 261 101 14 4
0 0 1 12301 22992 4400 1229 310 55 12 1
0 0 1 57628 338356 90870 17281 5145 948 220 36 4
0 0 0 185836 4692045 2013271 321788 84159 17894 3516 799 118 20 1
0 0 0 341797 62398297 45891477 7325370 1558408 344829 63072 14082 2665 466 66 6
0 0 0 298821 805690750 1059325766 187592813 32867106 7116021 1271737 253582 52710 9503 1779 245 30 1
		

Links

• Hugo Pfoertner, Table (flattened) of n, a(n) for n = 2..104 (rows 2..13).
• F. C. Bussemaker, S. Cobeljic, L. M. Cvetkovic and J. J. Seidel, Computer investigations of cubic graphs, T.H.-Report 76-WSK-01, Technological University Eindhoven, Dept. Mathematics, 1976.
• M. Meringer, GenReg, Generation of regular graphs.
• Gordon Royle, Cubic Graphs, October 1996.

Crossrefs

Cf. A002851, A294732.

Extensions

Extended using data from Gordon Royle's Cubic Graphs page by Hugo Pfoertner, Dec 13 2017