

A289989


Number of connected graphs of degree at most 4 with n nodes of degree at least 2.


2



1, 0, 0, 1, 3, 11, 38, 163, 884, 5621, 41971, 355823, 3360794, 34734530, 388337048
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OFFSET

0,5


COMMENTS

Also counts number of ncycloalkanes and single bonded allotropes with n carbon atoms.
Stereoisomerism is not taken into account. Some of the drawn structures may or may not exist due to their strained geometries.


LINKS

Table of n, a(n) for n=0..14.


EXAMPLE

a(4) = 3, because here are 3 molecules with 4 carbons following the above rule: cyclobutane, bicyclobutane, tetrahedrane.
a(5) = 11, because there are 11 molecules with 5 carbons following above rule: cyclopentane, housane, spiropentane, pyramidane, bicyclopentane, propellane, tricyclo[2.1.0.0^(1,3)]pentane, tricyclo[2.1.0.0^(2,5)]pentane tetracyclopentane, pentacyclopentane, hexacyclopentane.


PROG

(nauty/bash) geng c D4 d2 ${n} q  multig m1 D4 u


CROSSREFS

Cf. A121941, A289990, A289991.
Sequence in context: A047096 A149060 A151468 * A295263 A018961 A178624
Adjacent sequences: A289986 A289987 A289988 * A289990 A289991 A289992


KEYWORD

nonn,more


AUTHOR

Natan Arie' Consigli, Aug 03 2017


STATUS

approved



