A109111 - OEIS

A109111

a(n) = (1/sqrt(595))*((sqrt(595) + 26)*(125 + 5*sqrt(595))^n + (sqrt(595) - 26)*(125 - 5*sqrt(595))^n).

2, 510, 126000, 31117500, 7684875000, 1897880625000, 468706500000000, 115753214531250000, 28586773757812500000, 7059878528554687500000, 1743529551820312500000000, 430587479058662109375000000

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OFFSET

0,1

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. 292).

LINKS

Table of n, a(n) for n=0..11.

Index entries for linear recurrences with constant coefficients, signature (250,-750).

FORMULA

G.f.: 2(1+5z)/(1 - 250z + 750z^2).

MAPLE

a:=n->(1/sqrt(595))*((sqrt(595)+26)*(125+5*sqrt(595))^n+(sqrt(595)-26)*(125-5*sqrt(595))^n): seq(expand(a(n)), n=0..13);

MATHEMATICA

LinearRecurrence[{250, -750}, {2, 510}, 20] (* Harvey P. Dale, May 08 2025 *)

CROSSREFS

Sequence in context: A253706 A109032 A362539 * A004886 A234606 A139302

Adjacent sequences: A109108 A109109 A109110 * A109112 A109113 A109114

KEYWORD

nonn,easy

AUTHOR

Emeric Deutsch, Jun 19 2005

STATUS

approved