

A122679


Related to number of ncircumC_5 H_5 systems.


1



0, 5, 25, 80, 225, 605, 1600, 4205, 11025, 28880, 75625, 198005, 518400, 1357205, 3553225, 9302480, 24354225, 63760205, 166926400, 437019005, 1144130625, 2995372880, 7841988025, 20530591205, 53749785600, 140718765605, 368406511225, 964500768080
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OFFSET

1,2


LINKS

Colin Barker, Table of n, a(n) for n = 1..1000
J. Brunvoll, S. J. Cyvin and B. N. Cyvin, Azulenoids, MATCH, No. 34, 1996, 91108.
Index entries for linear recurrences with constant coefficients, signature (4,4,1).


FORMULA

a(n) = 15*Fibonacci(2*k1)5*Fibonacci(2*k)10 = 5*A004146(n1).
G.f.: 5*x^2*(1+x) / ( (x1)*(x^23*x+1) ).  R. J. Mathar, Nov 23 2014
a(1)=0, a(2)=5, a(3)=25, a(n) = 4*a(n1)4*a(n2)+a(n3).  Harvey P. Dale, Apr 21 2015
a(n) = 5*2^(1n)*(2^(2+n)(3sqrt(5))^n*(3+sqrt(5))+(3+sqrt(5))*(3+sqrt(5))^n).  Colin Barker, Nov 03 2016


MATHEMATICA

LinearRecurrence[{4, 4, 1}, {0, 5, 25}, 40] (* Harvey P. Dale, Apr 21 2015 *)


PROG

(PARI) concat(0, Vec(5*x^2*(1+x)/((x1)*(x^23*x+1)) + O(x^40))) \\ Colin Barker, Nov 03 2016


CROSSREFS

Sequence in context: A243303 A238449 A062989 * A264132 A147114 A296669
Adjacent sequences: A122676 A122677 A122678 * A122680 A122681 A122682


KEYWORD

nonn,easy


AUTHOR

N. J. A. Sloane, Sep 23 2006


EXTENSIONS

More terms from Harvey P. Dale, Apr 21 2015


STATUS

approved



