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A167779
Subsequence of A167708 whose indices are congruent to 4 mod 5, i.e., a(n) = A167708(5n+4).
7
105, 35634, 12115455, 4119219066, 1400522366985, 476173485555834, 161897584566616575, 55044702579164079666, 18715036979331220469865, 6363057528270035795674434, 2163420844574832839308837695, 735556724097914895329209141866, 250087122772446489579091799396745
OFFSET
0,1
FORMULA
a(n+2) = 340*a(n+1) - a(n).
a(n+1) = 170*a(n) + 39*sqrt(19*a(n)^2 - 1539).
G.f.: (105 - 66*z)/(1 - 340*z + z^2).
a(n) = ((105 + 24*sqrt(19))/2)*(170 + 39*sqrt(19))^(n) + ((105 - 24*sqrt(19) )/2)*(170 - 39*sqrt(19))^(n).
EXAMPLE
a(0) = A167708(4) = 105, a(1) = A167708(9) = 35634, ...
MAPLE
u(0):=105:u(1):=35634:for n from 0 to 20 do u(n+2):=340*u(n+1)-u(n):od:seq(u(n), n=0..20); taylor(((105+35634*z-105*z*340)/(1-340*z+z^2)), z=0, 20); for n from 0 to 20 do u(n):=simplify((24*sqrt(19)+105)/2*(170+39*sqrt(19))^(n)+(-24*sqrt(19)+105)/2*(170-39*sqrt(19))^(n)):od:seq(u(n), n=0..20);
MATHEMATICA
LinearRecurrence[{340, -1}, {105, 35634}, 50] (* G. C. Greubel, Jun 23 2016 *)
PROG
(Magma) I:=[105, 35634]; [n le 2 select I[n] else 340*Self(n-1)-Self(n-2): n in [1..20]]; // Vincenzo Librandi, Jun 25 2016
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Richard Choulet, Nov 11 2009
STATUS
approved