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A289990 Number of connected graphs of degree at most 4 with n nodes of degree at least 2 which are not 4-regular graphs. 2
1, 0, 0, 1, 3, 10, 37, 161, 878, 5605, 41912, 355558, 3359250, 34723752, 388248880 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

This is the number of pure n-cycloalkylic 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

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Last modified July 17 23:21 EDT 2019. Contains 325109 sequences. (Running on oeis4.)