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A136010 a(0)=20, a(1)=9; for n >= 0, a(n+2) = 7*a(n+1) + 9*a(n). 1
20, 9, 243, 1782, 14661, 118665, 962604, 7806213, 63306927, 513404406, 4163593185, 33765791949, 273832882308, 2220722303697, 18009552066651, 146053365199830, 1184459524998669, 9605696961789153, 77900014457512092 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

From an online IQ test (Adaptive IQ).

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (7,9).

FORMULA

G.f.: (20 - 131*x)/(1-7*x-9*x^2). - M. F. Hasler, Mar 27 2008

a(n) = (10 + 61/sqrt(85))*(7/2 - sqrt(85)/2)^n + (10 - 61/sqrt(85))*(7/2 + sqrt(85)/2)^n. - Alexander R. Povolotsky, simplified by M. F. Hasler, Mar 29 2008

MAPLE

A136010:=n -> simplify((10+61/sqrt(85))*(7/2-1/2*sqrt(85))^n+(10-61/sqrt(85))*(7/2+1/2*sqrt(85))^n); # M. F. Hasler, Mar 29 2008

MATHEMATICA

LinearRecurrence[{7, 9}, {20, 9}, 50] (* G. C. Greubel, Feb 21 2017 *)

PROG

(PARI) A136010(n) = { local(y=Mod(x, x^2-85)); lift((10+61/y)*(7/2-1/2*y)^n+(10-61/y)*(7/2+1/2*y)^n)} \\ M. F. Hasler, improved by Max Alekseyev, Mar 29 2008

(PARI) x='x+O('x^50); Vec((20 - 131*x)/(1-7*x-9*x^2)) \\ G. C. Greubel, Feb 21 2017

CROSSREFS

Sequence in context: A040384 A078080 A216289 * A091534 A033966 A033340

Adjacent sequences:  A136007 A136008 A136009 * A136011 A136012 A136013

KEYWORD

nonn,easy

AUTHOR

Jordan Giedd (jordyg365(AT)gmail.com), Mar 20 2008

EXTENSIONS

Definition supplied by Don Reble, Mar 27 2008

STATUS

approved

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Last modified May 15 17:50 EDT 2021. Contains 343920 sequences. (Running on oeis4.)