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A006627 Number of nonisomorphic 2-graphs with n nodes with first and second cohomology invariants both 0.
(Formerly M0842)
2
1, 1, 2, 3, 7, 14, 54, 224, 2038, 32728 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 18 10:19 EDT 2021. Contains 343995 sequences. (Running on oeis4.)