

A123544


Number of connected labeled 2regular relations of order n.


5



0, 0, 1, 6, 87, 1980, 66270, 3050460, 184716630, 14231775600, 1359481407480, 157694893448400, 21835679256606600, 3557942554594428000, 673941365091485290800, 146851484638349504613600
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OFFSET

0,4


REFERENCES

R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1982.


LINKS

R. W. Robinson, Table of n, a(n) for n = 0..48


FORMULA

E.g.f.: log(1 + Sum_{k>0} A001499(k)*x^k/k!).  Andrew Howroyd, Sep 09 2018


MATHEMATICA

m = 16;
a1499[n_] := (n  1)*n!*Gamma[n  1/2]*Hypergeometric1F1[2  n, 3/2  n, 1/2]/Sqrt[Pi];
egf = Log[1 + Sum[a1499[k] x^k/k!, {k, 1, m}]];
CoefficientList[egf + O[x]^m, x] Range[0, m1]! (* JeanFrançois Alcover, Aug 26 2019 *)


PROG

(PARI) seq(n)={Vec(serlaplace(log(serlaplace(exp(x/2 + O(x*x^n))/sqrt(1x + O(x*x^n))))), (n+1))}; \\ Andrew Howroyd, Sep 09 2018


CROSSREFS

Connected version of A001499. Unlabeled version is A005642.
Cf. A123543.
Sequence in context: A249929 A289394 A113666 * A239749 A277337 A138216
Adjacent sequences: A123541 A123542 A123543 * A123545 A123546 A123547


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Nov 13 2006


STATUS

approved



