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A192797
Molecular topological indices of the cycle graphs
0
4, 12, 24, 48, 80, 132, 196, 288, 396, 540, 704, 912, 1144, 1428, 1740, 2112, 2516, 2988, 3496, 4080, 4704, 5412, 6164, 7008, 7900, 8892, 9936, 11088, 12296, 13620, 15004, 16512, 18084, 19788, 21560, 23472, 25456, 27588, 29796, 32160, 34604
OFFSET
1,1
COMMENTS
Cycle graphs defined for n>=3; extended to n=1 using the closed form
FORMULA
a(n) = n*(2*n^2+(-1)^n+15)/4.
a(n) = +2*a(n-1) +1*a(n-2) -4*a(n-3) +1*a(n-4) +2*a(n-5) -1*a(n-6).
G.f.: 4*x*(1+x-x^2+x^3+x^4)/((1-x)^4*(1+x)^2).
PROG
(PARI) a(n)=n*(2*n^2+(-1)^n+15)/4;
CROSSREFS
Sequence in context: A372435 A321879 A328225 * A278355 A160619 A352668
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Jul 10 2011
STATUS
approved