%I A004104 M1649
%S A004104 1,1,2,6,20,86,662,8120,171526,5909259,348089533,33883250874,
%T A004104 5476590066777,1490141905609371,666003784522738152,
%U A004104 509204473666338077658,636051958071749028811326
%N A004104 Number of self-dual signed graphs with n nodes. Also number of self-complementary 
               2-multigraphs on n nodes.
%C A004104 A 2-multigraph is similar to an ordinary graph except there are 0, 1 
               or 2 edges between any two nodes (self-loops are not allowed).
%D A004104 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A004104 Harary, Frank; Palmer, Edgar M.; Robinson, Robert W.; Schwenk, Allen 
               J.; Enumeration of graphs with signed points and lines. J. Graph 
               Theory 1 (1977), no. 4, 295-308.
%D A004104 F. Harary and R. W. Robinson, Exposition of the enumeration of point-line-signed 
               graphs, pp. 19 - 33 of Proc. Second Caribbean Conference Combinatorics 
               and Computing (Bridgetown, 1977). Ed. R. C. Read and C. C. Cadogan. 
               University of the West Indies, Cave Hill Campus, Barbados, 1977. 
               vii+223 pp.
%D A004104 R. W. Robinson, personal communication.
%D A004104 R. W. Robinson, Numerical implementation of graph counting algorithms, 
               AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1976.
%H A004104 R. W. Robinson, <a href="b004104.txt">Table of n, a(n) for n = 1..22</
               a>
%Y A004104 Cf. A004102.
%Y A004104 Sequence in context: A117574 A115084 A089179 this_sequence A079468 A124382 
               A000666
%Y A004104 Adjacent sequences: A004101 A004102 A004103 this_sequence A004105 A004106 
               A004107
%K A004104 nonn,nice
%O A004104 1,3
%A A004104 N. J. A. Sloane (njas(AT)research.att.com).
%E A004104 More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 19 2000