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A108646 a(n) = (n+1)(n+2)^2*(n+3)(11n^3 + 58n^2 + 101n + 60)/720. 1
1, 23, 194, 985, 3668, 11074, 28728, 66438, 140415, 276001, 511082, 900263, 1519882, 2473940, 3901024, 5982300, 8950653, 13101051, 18802210, 26509637, 36780128, 50287798, 67841720, 90405250, 119117115, 155314341, 200557098 (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, no. 22).

LINKS

Chai Wah Wu, Table of n, a(n) for n = 0..10000

FORMULA

From Chai Wah Wu, Jun 12 2016: (Start)

a(n) = 8*a(n-1) - 28*a(n-2) + 56*a(n-3) - 70*a(n-4) + 56*a(n-5) - 28*a(n-6) + 8*a(n-7) - a(n-8) for n > 7.

G.f.: (2*x^4 + 21*x^3 + 38*x^2 + 15*x + 1)/(x - 1)^8. (End)

MAPLE

a:=(n+1)*(n+2)^2*(n+3)*(11*n^3+58*n^2+101*n+60)/720: seq(a(n), n=0..30);

PROG

(Python)

A108646_list, m = [], [77, -85, 28, -1, 1, 1, 1, 1]

for _ in range(10001):

    A108646_list.append(m[-1])

    for i in range(7):

        m[i+1] += m[i] # Chai Wah Wu, Jun 12 2016

CROSSREFS

Sequence in context: A160083 A140545 A062640 * A307355 A058193 A065314

Adjacent sequences:  A108643 A108644 A108645 * A108647 A108648 A108649

KEYWORD

nonn

AUTHOR

Emeric Deutsch, Jun 13 2005

STATUS

approved

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Last modified July 23 15:55 EDT 2019. Contains 325258 sequences. (Running on oeis4.)