

A054920


Number of connected unlabeled reflexive relations with n nodes such that complement is also connected.


1



2, 4, 68, 2592, 278796, 95720106, 111891292036, 457846756500066, 6664787020904248568, 349363873490889302878250, 66602024342830108271942323060, 46557190064705399729526041154647820
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OFFSET

1,1


LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..50
V. A. Liskovets, Some easily derivable sequences, J. Integer Sequences, 3 (2000), #00.2.2.


FORMULA

a(n) = 2*A054919(n)  A000595(n).


CROSSREFS

Cf. A000595, A054919.
Sequence in context: A018364 A100603 A301818 * A062061 A066974 A270583
Adjacent sequences: A054917 A054918 A054919 * A054921 A054922 A054923


KEYWORD

nonn,easy


AUTHOR

N. J. A. Sloane, May 24 2000


EXTENSIONS

More terms from Vladeta Jovovic, Jul 17 2000


STATUS

approved



