A126123 Triangle read by rows: T(n,k) = number of edge-rooted unlabeled graphs having n nodes and k edges, n > 0, 0 < k <= n*(n-1)/2.

0, 1, 1, 1, 1, 1, 2, 4, 4, 2, 1, 1, 2, 6, 12, 16, 16, 12, 6, 2, 1, 1, 2, 7, 18, 40, 68, 96, 108, 96, 68, 40, 18, 7, 2, 1, 1, 2, 7, 20, 56, 135, 281, 500, 764, 982, 1068, 982, 764, 500, 281, 135, 56, 20, 7, 2, 1, 1, 2, 7, 21, 63, 181, 485, 1159, 2499, 4788, 8074, 11967, 15566

Offset

1,7

References

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973.

Links

Table of n, a(n) for n=1..70.

Example

0;
1;
1,1,1;
1,2,4,4,2,1;
1,2,6,12,16,16,12,6,2,1;
1,2,7,18,40,68,96,108,96,68,40,18,7,2,1;

Crossrefs

Cf. A126122 (row sums).

Sequence in context: A070512 A156346 A156283 * A285349 A256066 A096832

Adjacent sequences: A126120 A126121 A126122 * A126124 A126125 A126126

Keyword

nonn,tabf

Author

Vladeta Jovovic, Mar 07 2007

Status

approved