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A123358
Kekulé numbers for certain benzenoids (see the Cyvin-Gutman book for details).
2
1, 10, 125, 1625, 21250, 278125, 3640625, 47656250, 623828125, 8166015625, 106894531250, 1399267578125, 18316650390625, 239768066406250, 3138604736328125, 41084869384765625, 537807922363281250, 7039997100830078125, 92154758453369140625, 1206321449279785156250, 15790952777862548828125, 206706255435943603515625
OFFSET
0,2
LINKS
S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (see p. 210, formula page 204).
FORMULA
G.f.: -(5*x-1) / (25*x^2-15*x+1). - Colin Barker, Aug 29 2013
a(n) = 5^n*A001519(n+1). - R. J. Mathar, Jul 26 2019
MAPLE
A123358 := proc(n)
option remember;
if n <= 1 then
op(n+1, [1, 10]) ;
else
15*procname(n-1)-25*procname(n-2) ;
end if
end proc:
seq( A123358(n), n=0..30) ; # R. J. Mathar, Jul 26 2019
MATHEMATICA
LinearRecurrence[{15, -25}, {1, 10}, 30] (* Jean-François Alcover, Apr 03 2020 *)
CROSSREFS
Cf. A001519.
Sequence in context: A005174 A034668 A215854 * A230390 A089832 A161170
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Oct 10 2006
STATUS
approved