

A132584


a(0)=0, a(1)=4; for n > 1, a(n) = 18*a(n1)  a(n2) + 8.


4



0, 4, 80, 1444, 25920, 465124, 8346320, 149768644, 2687489280, 48225038404, 865363202000, 15528312597604, 278644263554880, 5000068431390244, 89722587501469520, 1610006506595061124, 28890394531209630720, 518417095055178291844, 9302617316461999622480
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OFFSET

0,2


COMMENTS

The old definition given for this sequence was "Sequence allows us to find X values of the equation: X(X + 1)  5*Y^2 = 0".


LINKS

Seiichi Manyama, Table of n, a(n) for n = 0..500
Index entries for linear recurrences with constant coefficients, signature (19,19,1).


FORMULA

a(n) = 1/2 + (1/4)*(94*sqrt(5))^n + (1/4)*(9+4*sqrt(5))^n.  Paolo P. Lava, Oct 07 2008
a(n) = (A023039(n)  1)/2.  Max Alekseyev, Nov 13 2009
G.f.: 4*x*(x+1)/((x1)*(x^218*x+1)).  Colin Barker, Oct 24 2012


MATHEMATICA

LinearRecurrence[{19, 19, 1}, {0, 4, 80}, 40] (* Vincenzo Librandi, Dec 24 2018 *)


PROG

(MAGMA) I:=[0, 4, 80]; [n le 3 select I[n] else 18*Self(n1)Self(n2)+8: n in [1..30]]; // Vincenzo Librandi, Dec 24 2018


CROSSREFS

Cf. A007654.
Sequence in context: A054322 A114488 A055787 * A277074 A012127 A189791
Adjacent sequences: A132581 A132582 A132583 * A132585 A132586 A132587


KEYWORD

nonn,easy


AUTHOR

Mohamed Bouhamida, Nov 14 2007


EXTENSIONS

More terms from Max Alekseyev, Nov 13 2009
New definition by Antti Karttunen, Oct 24 2012


STATUS

approved



