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A107971 a(n) = (n+1)(n+2)(n+3)(35n^3 + 153n^2 + 232n + 120)/720. 0
1, 18, 123, 523, 1673, 4424, 10206, 21246, 40821, 73546, 125697, 205569, 323869, 494144, 733244, 1061820, 1504857, 2092242, 2859367, 3847767, 5105793, 6689320, 8662490, 11098490, 14080365, 17701866, 22068333, 27297613, 33521013, 40884288 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Kekulé numbers for certain benzenoids.

REFERENCES

S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (p. 230).

LINKS

Table of n, a(n) for n=0..29.

FORMULA

From R. J. Mathar, Apr 07 2008: (Start)

O.g.f.: -(1 + 11x + 18x^2 + 5x^3)/(-1+x)^7.

a(n) = A107962(n) - A107962(n-1). (End)

MAPLE

a:=n->(1/720)*(n+1)*(n+2)*(n+3)*(35*n^3+153*n^2+232*n+120): seq(a(n), n=0..35);

CROSSREFS

Sequence in context: A223046 A037064 A077960 * A292314 A002424 A101378

Adjacent sequences:  A107968 A107969 A107970 * A107972 A107973 A107974

KEYWORD

nonn,easy

AUTHOR

Emeric Deutsch, Jun 12 2005

STATUS

approved

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Last modified January 22 16:37 EST 2020. Contains 331152 sequences. (Running on oeis4.)