

A123550


Triangle read by rows: T(n,k) = number of unlabeled connected bicolored graphs having 2n nodes and k edges, which are invariant when the two color classes are interchanged. Here n >= 0, 0 <= k <= n^2.


2



0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 2, 2, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 4, 6, 6, 6, 5, 4, 2, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 15, 23, 31, 36, 34, 31, 27, 21, 14, 9, 6, 4, 2, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 20, 44, 84, 134, 196, 249, 288, 313, 317, 303, 267, 224, 180
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OFFSET

1,13


REFERENCES

R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1978.


LINKS

R. W. Robinson, Rows 0 through 7, flattened


EXAMPLE

Triangle begins:
n = 1
k = 0 : 0
k = 1 : 1
Total = 1
n = 2
k = 0 : 0
k = 1 : 0
k = 2 : 0
k = 3 : 1
k = 4 : 1
Total = 2
n = 3
k = 0 : 0
k = 1 : 0
k = 2 : 0
k = 3 : 0
k = 4 : 0
k = 5 : 2
k = 6 : 2
k = 7 : 1
k = 8 : 1
k = 9 : 1
Total = 7


CROSSREFS

Sequence in context: A321400 A004562 A261817 * A320638 A262045 A263087
Adjacent sequences: A123547 A123548 A123549 * A123551 A123552 A123553


KEYWORD

nonn,tabf


AUTHOR

N. J. A. Sloane, Nov 14 2006


STATUS

approved



