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

0,5

COMMENTS

Also counts number of n-cycloalkanes 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

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Last modified July 17 02:10 EDT 2019. Contains 325092 sequences. (Running on oeis4.)