A005976 Number of unlabeled connected interval graphs with n nodes. (Formerly M1487)

1, 1, 2, 5, 15, 56, 250, 1328, 8069, 54962, 410330, 3317302, 28774874, 266242936, 2616100423, 27205605275, 298569256590, 3449309394415, 41854968275924, 532353636671777, 7083840662453415, 98443312509634266, 1426382369328881332

Offset

1,3

References

P. J. Hanlon, personal communication.

R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1980.

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

Links

R. W. Robinson, Table of n, a(n) for n = 1..30

Phil Hanlon, Counting interval graphs, Trans. Amer. Math. Soc. 272 (1982), no. 2, 383-426.

Crossrefs

Sequence in context: A137533 A121392 A216388 * A351158 A187981 A334155

Adjacent sequences: A005973 A005974 A005975 * A005977 A005978 A005979

Keyword

nonn,nice

Author

N. J. A. Sloane

Extensions

a(21) onwards added by N. J. A. Sloane, Oct 19 2006 from the Robinson reference

Status

approved