

A123543


Number of connected labeled 2regular pseudodigraphs (multiple arcs and loops allowed) of order n.


4



0, 1, 2, 14, 201, 4704, 160890, 7538040, 462869190, 36055948320, 3474195588360, 405786523413600, 56502317464777800, 9248640671612865600, 1758505909558569771600, 384399253128691423022400
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OFFSET

0,3


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} A000681(k)*x^k/k!).  Andrew Howroyd, Sep 09 2018


MATHEMATICA

m = 16;
a681[n_] := n!*HypergeometricPFQ[{1/2, n}, {}, 2]/2^n;
egf = Log[1 + Sum[a681[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 A000681.
First column of A307804.
Cf. A123544.
Sequence in context: A213977 A322196 A102224 * A279452 A262008 A054652
Adjacent sequences: A123540 A123541 A123542 * A123544 A123545 A123546


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Nov 13 2006


STATUS

approved



