A006627 Number of nonisomorphic 2-graphs with n nodes with first and second cohomology invariants both 0. (Formerly M0842)

1, 1, 2, 3, 7, 14, 54, 224, 2038, 32728

Offset

1,3

References

Buekenhout, ed., Handbook of Incidence Geometry, 1995, p. 884.

J. J. Seidel and D. E. Taylor, Two-graphs: a second survey, pp. 689-711 of L. Lovasz and V. Sos, eds., Algebraic Methods in Graph Theory (Colloq. Janos Bolyai 25), North-Holland, 1981.

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

Links

Table of n, a(n) for n=1..10.

F. C. Bussemaker, R. A. Mathon and J. J. Seidel, Tables of two-graphs, 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.

F. C. Bussemaker, R. A. Mathon and J. J. Seidel, Tables of two-graphs, 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.

Crossrefs

Cf. A085617, A002854.

Sequence in context: A238728 A271718 A222626 * A077161 A068080 A276600

Adjacent sequences: A006624 A006625 A006626 * A006628 A006629 A006630

Keyword

nonn,nice

Author

N. J. A. Sloane

Status

approved