

A289991


Number of unlabeled connected simple graphs with n nodes of degree 4 or less and with at least a cyclic structure and a node of degree one.


2



0, 0, 0, 1, 7, 35, 181, 1027, 6551, 47356, 383353, 3439508, 33796286, 360254030, 4132780425, 50700507116, 661702767423, 9148018231984, 133481943863634, 2049205561735698, 33008193951255524, 556509843849858317, 9799223447550907197, 179855583136712491494
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OFFSET

1,5


COMMENTS

Number of alkylncycloalkanes with n carbon atoms (the pure ncycloalkanes aren't counted here).
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=1..24.


FORMULA

a(n) = A289159(n)  A289990(n).
a(n) = A121941(n)  A006820(n)  A289989(n).  Andrew Howroyd, Mar 20 2020


EXAMPLE

a(5) = 7 because there are 7 structures with 5 carbons following the rule above: 1,1dimethylcyclopropane, 1,2dimethylcyclopropane, ethylcyclopropane, methylcyclobutane, 1methylbicyclobutane, 2methylbicyclobutane, methyltetrahedrane.


CROSSREFS

Cf. A006820, A121941, A289159, A289989, A289990.
Sequence in context: A037689 A051926 A297602 * A295248 A295647 A026128
Adjacent sequences: A289988 A289989 A289990 * A289992 A289993 A289994


KEYWORD

nonn


AUTHOR

Natan Arie Consigli, Aug 03 2017


EXTENSIONS

a(0) removed and a(15)a(24) from Andrew Howroyd, Mar 20 2020


STATUS

approved



