%I
%S 1,1,4,0,19,10
%N Number of selfcomplementary 2graphs with n nodes.
%C Sozański (1980, p. 141) says: "Note that formula (20) also gives the number of isomorphism classes of selfcomplementary ppoint twographs." 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 twographs</a>, T.H.Report 79WSK05, Technological University Eindhoven, Dept. Mathematics, 1979; also pp. 71112 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 twographs</a>, T.H.Report 79WSK05, Technological University Eindhoven, Dept. Mathematics, 1979; also pp. 71112 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, 127144.
%Y Cf. A002854, A006627, A263626.
%K nonn,more
%O 4,3
%A _N. J. A. Sloane_, Jul 11 2003
