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A107970 a(n) = (n+1)*(n+2)^3*(n+3)*(2n+3)*(2n+5)/360. 0
1, 21, 168, 825, 3003, 8918, 22848, 52326, 109725, 214291, 394680, 692055, 1163799, 1887900, 2968064, 4539612, 6776217, 9897537, 14177800, 19955397, 27643539, 37742034, 50850240, 67681250, 89077365, 116026911, 149682456, 191380483 (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..27.

Index entries for linear recurrences with constant coefficients, signature (8,-28,56,-70,56,-28,8,-1).

FORMULA

G.f.: (x^4+13*x^3+28*x^2+13*x+1)/(x-1)^8. - Colin Barker, Sep 21 2012

MAPLE

a:=n->(1/360)*(n+1)*(n+2)^3*(n+3)*(2*n+3)*(2*n+5): seq(a(n), n=0..32);

CROSSREFS

Sequence in context: A126993 A022681 A266733 * A105249 A278992 A041848

Adjacent sequences:  A107967 A107968 A107969 * A107971 A107972 A107973

KEYWORD

nonn,easy

AUTHOR

Emeric Deutsch, Jun 12 2005

STATUS

approved

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Last modified January 21 13:47 EST 2020. Contains 331113 sequences. (Running on oeis4.)