A085618 - OEIS

%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&amp;gbpv=1&amp;pg=PA70&amp;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