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A108673
a(n) = (n+1)(n+2)(n+3)(2n+3)(10n^2 + 27n + 20)/360.
0
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
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).
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
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, Jun 17 2005
STATUS
approved