

A289990


Number of connected graphs of degree at most 4 with n nodes of degree at least 2 which are not 4regular graphs.


2



1, 0, 0, 1, 3, 10, 37, 161, 878, 5605, 41912, 355558, 3359250, 34723752, 388248880
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OFFSET

0,5


COMMENTS

This is the number of pure ncycloalkylic structures 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.


FORMULA

a(n) = A289989(n)  A006820(n).


EXAMPLE

a(4) = 3, because here are 3 molecules with 4 carbons following the above rule: cyclobutane, bicyclobutane, tetrahedrane.
a(5) = 10, because there are 10 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.


CROSSREFS

Cf. A006820, A121941, A289989, A289991.
Sequence in context: A005493 A138378 A250307 * A123636 A092816 A078109
Adjacent sequences: A289987 A289988 A289989 * A289991 A289992 A289993


KEYWORD

nonn,more


AUTHOR

Natan Arie' Consigli, Aug 03 2017


STATUS

approved



