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A065889
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a(n) = number of unicyclic connected simple graphs whose cycle has length 4.
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5
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3, 60, 1080, 20580, 430080, 9920232, 252000000, 7015381560, 212840939520, 6998969586180, 248180493969408, 9445533398437500, 384213343210045440, 16639691095281974160, 764619269867445288960, 37163398969133506235952
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OFFSET
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4,1
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LINKS
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FORMULA
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E.g.f.: T^4/8, where T = T(x) is Euler's tree function (see A000169).
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MATHEMATICA
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Table[12*Binomial[n, 4]*n^(n-5), {n, 4, 25}] (* G. C. Greubel, May 16 2019 *)
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PROG
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(PARI) {a(n) = 12*binomial(n, 4)*n^(n-5)}; \\ G. C. Greubel, May 16 2019
(Magma) [12*Binomial(n, 4)*n^(n-5) : n in [4..25]]; // G. C. Greubel, May 16 2019
(Sage) [12*binomial(n, 4)*n^(n-5) for n in (4..25)] # G. C. Greubel, May 16 2019
(GAP) List([4..25], n-> 12*Binomial(n, 4)*n^(n-5)) # G. C. Greubel, May 16 2019
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CROSSREFS
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A065888 ( = 2*A065889) counts sagittal graphs with one cycle (length 4).
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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