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%I #18 Mar 02 2021 04:53:18
%S 1,1,4,0,19,10
%N Number of self-complementary 2-graphs with n nodes.
%C Sozański (1980, p. 141) says: "Note that formula (20) also gives the number of isomorphism classes of self-complementary p-point two-graphs." Formula (20) apparently refers to sequence A263626 (according to the references there). Is this sequence the same as A263626? (This would mean a(n) = 0 for 3 == n mod 4.) - _Petros Hadjicostas_, Feb 27 2021
%H F. C. Bussemaker, R. A. Mathon and J. J. Seidel, <a href="https://link.springer.com/content/pdf/10.1007/BFb0092256.pdf">Tables of two-graphs</a>, T.H.-Report 79-WSK-05, Technological University Eindhoven, Dept. Mathematics, 1979; also pp. 71-112 of "Combinatorics and Graph Theory (Calcutta, 1980)", Lect. Notes Math. 885, 1981.
%H F. C. Bussemaker, R. A. Mathon and J. J. Seidel, <a href="https://www.google.com/books/edition/Combinatorics_and_Graph_Theory/KD17CwAAQBAJ?hl=en&gbpv=1&pg=PA70&printsec=frontcover">Tables of two-graphs</a>, T.H.-Report 79-WSK-05, Technological University Eindhoven, Dept. Mathematics, 1979; also pp. 71-112 of "Combinatorics and Graph Theory (Calcutta, 1980)", Lect. Notes Math. 885, 1981.
%H Tadeusz Sozański, <a href="https://doi.org/10.1002/jgt.3190040202">Enumeration of weak isomorphism classes of signed graphs</a>, J. Graph Theory 4 (1980), no. 2, 127-144.
%Y Cf. A002854, A006627, A263626.
%K nonn,more
%O 4,3
%A _N. J. A. Sloane_, Jul 11 2003
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