A108673 - OEIS

A108673

a(n) = (n+1)(n+2)(n+3)(2n+3)(10n^2 + 27n + 20)/360.

1, 19, 133, 573, 1848, 4914, 11382, 23766, 45771, 82621, 141427, 231595, 365274, 557844, 828444, 1200540, 1702533, 2368407, 3238417, 4359817, 5787628, 7585446, 9826290, 12593490, 15981615, 20097441, 25060959, 31006423, 38083438, 46458088

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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. 231, # 31).

LINKS

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

Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).

FORMULA

G.f.: (1 + 12z + 21z^2 + 6z^3)/(1-z)^7.

MAPLE

a:=n->(n+1)*(n+2)*(n+3)*(2*n+3)*(10*n^2+27*n+20)/360: seq(a(n), n=0..32);

CROSSREFS

Sequence in context: A142649 A020867 A022679 * A041692 A078977 A085464

Adjacent sequences: A108670 A108671 A108672 * A108674 A108675 A108676

KEYWORD

nonn,easy

AUTHOR

Emeric Deutsch, Jun 17 2005

STATUS

approved