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A261174 Number of multigraphs on 4 unlabeled nodes with n edges where the edges can be of two colors. 0
1, 2, 9, 30, 90, 248, 650, 1560, 3560, 7680, 15786, 31076, 58905, 107768, 191180, 329664, 554038, 909558, 1461655, 2302950, 3563482, 5422392, 8124040, 11997648, 17482295, 25156872 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..25.

MATHEMATICA

Needs["Combinatorica`"]; n = 4; nn = 25; CoefficientList[Series[PairGroupIndex[SymmetricGroup[n], s] /.Table[s[i] -> 1/(1 - x^i)^2, {i, 1, Binomial[n, 2]}], {x, 0, nn}], x]

CROSSREFS

Cf. A050531.

Sequence in context: A290746 A268586 A056288 * A273652 A056283 A192518

Adjacent sequences:  A261171 A261172 A261173 * A261175 A261176 A261177

KEYWORD

nonn

AUTHOR

Geoffrey Critzer, Aug 10 2015

STATUS

approved

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Last modified November 20 02:52 EST 2018. Contains 317370 sequences. (Running on oeis4.)