A005974 - OEIS

A005974

Number of unlabeled connected identity interval graphs with n nodes.
(Formerly M3617)

1, 0, 0, 0, 0, 4, 27, 172, 1141, 8017, 60319, 486372, 4196384, 38621356, 377949874, 3920335179, 42975606304, 496545261764, 6031989895262, 76867521958187, 1025417405366410, 14292224499308110, 207763603833695113, 3144818752057400765

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,6

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.

PROG

(Sage) def a(n) : return sum(G.is_connected() and G.is_interval() and G.automorphism_group().order()==1 for G in graphs(n)) # Eric M. Schmidt, Mar 25 2015

CROSSREFS

Sequence in context: A306054 A218274 A061693 * A289718 A010910 A078100

Adjacent sequences: A005971 A005972 A005973 * A005975 A005976 A005977

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

Definition edited by Eric M. Schmidt, Mar 25 2015

STATUS

approved