cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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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.

Original entry on oeis.org

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

Views

Author

Natan Arie Consigli, Aug 03 2017

Keywords

Comments

Number of alkyl-n-cycloalkanes with n carbon atoms (the pure n-cycloalkanes 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.

Examples

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

Crossrefs

Cf. A006820, A121941, A289159, A289989, A289990.

Formula

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

Extensions

a(0) removed and a(15)-a(24) from Andrew Howroyd, Mar 20 2020
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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