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A000171 Number of self-complementary graphs with n nodes.
(Formerly M0014 N0780)
12
1, 0, 0, 1, 2, 0, 0, 10, 36, 0, 0, 720, 5600, 0, 0, 703760, 11220000, 0, 0, 9168331776, 293293716992, 0, 0, 1601371799340544, 102484848265030656, 0, 0, 3837878966366932639744, 491247277315343649710080, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

a(n) = A007869(n)-A054960(n), where A007869(n) is number of unlabeled graphs with n nodes and an even number of edges and A054960(n) is number of unlabeled graphs with n nodes and an odd number of edges.

REFERENCES

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 139, Table 6.1.1.

R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..100

H. Fripertinger, Self-complementary graphs

Richard A. Gibbs, Self-complementary graphs J. Combinatorial Theory Ser. B 16 (1974), 106--123. MR0347686 (50 #188). - N. J. A. Sloane, Mar 27 2012

B. D. McKay, Self-complementary graphs

R. C. Read, On the number of self-complementary graphs and digraphs, J. London Math. Soc., 38 (1963), 99-104.

Eric Weisstein's World of Mathematics, Self-Complementary Graph

D. Wille, Enumeration of self-complementary structures, J. Comb. Theory B 25 (1978) 143-150

FORMULA

a(4n) = A003086(2n).

a(4*n+1) = A047832(n), a(4*n+2) = a(4*n+3) = 0. - Andrew Howroyd, Sep 16 2018

MATHEMATICA

<<Combinatorica`; Table[GraphPolynomial[n, x]/.x -> -1, {n, 1, 20}]  (* Geoffrey Critzer, Oct 21 2012 *)

permcount[v_] := Module[{m = 1, s = 0, k = 0, t}, For[i = 1, i <= Length[v], i++, t = v[[i]]; k = If[i > 1 && t == v[[i - 1]], k + 1, 1]; m *= t*k; s += t]; s!/m];

edges[v_] := 4 Sum[Sum[GCD[v[[i]], v[[j]]], {j, 1, i - 1}], {i, 2, Length[v]}] + 2 Total[v];

a[n_] := Module[{s = 0}, Switch[Mod[n, 4], 2|3, 0, _, Do[s += permcount[4 p]*2^edges[p]*If[OddQ[n], n*2^Length[p], 1], {p, IntegerPartitions[ Quotient[n, 4]]}]; s/n!]];

Array[a, 40] (* Jean-Fran├žois Alcover, Aug 26 2019, after Andrew Howroyd *)

PROG

(PARI)

permcount(v) = {my(m=1, s=0, k=0, t); for(i=1, #v, t=v[i]; k=if(i>1&&t==v[i-1], k+1, 1); m*=t*k; s+=t); s!/m}

edges(v) = {4*sum(i=2, #v, sum(j=1, i-1, gcd(v[i], v[j]))) + 2*sum(i=1, #v, v[i])}

a(n) = {my(s=0); if(n%4<2, forpart(p=n\4, s+=permcount(4*Vec(p)) * 2^edges(p) * if(n%2, n*2^#p, 1))); s/n!} \\ Andrew Howroyd, Sep 16 2018

CROSSREFS

Cf. A047660, A051251, A047832.

Cf. A008406 (triangle of coefficients of the "graph polynomial").

Sequence in context: A181501 A213704 A278099 * A054922 A289651 A302751

Adjacent sequences:  A000168 A000169 A000170 * A000172 A000173 A000174

KEYWORD

nonn,nice

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from R. C. Read (rcread(AT)math.uwaterloo.ca) and Vladeta Jovovic

STATUS

approved

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Last modified October 16 06:34 EDT 2019. Contains 328051 sequences. (Running on oeis4.)