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A002063 9*4^n. 18
9, 36, 144, 576, 2304, 9216, 36864, 147456, 589824, 2359296, 9437184, 37748736, 150994944, 603979776, 2415919104, 9663676416, 38654705664, 154618822656, 618475290624, 2473901162496, 9895604649984, 39582418599936, 158329674399744, 633318697598976 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(n) is twice the area of the trapezoid created by the four points (2^n,2^(n+1)), (2^(n+1), 2^n),  (2^(n+1), 2^(n+2)),  (2^(n+2), 2^(n+1)). - J. M. Bergot, May 23 2014

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..500

Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

Tanya Khovanova, Recursive Sequences

Index to sequences with linear recurrences with constant coefficients, signature (4).

FORMULA

a(n)=4*a(n-1), n>0; a(0)=9. G.f.: 9/(1-4*x). - Philippe Deléham, Nov 23 2008

MATHEMATICA

9*4^Range[0, 100] (* Vladimir Joseph Stephan Orlovsky, Jun 09 2011 *)

PROG

(MAGMA) [9*4^n: n in [0..30]]; // Vincenzo Librandi, May 19 2011

(PARI) a(n)=9<<n \\ Charles R Greathouse IV, Apr 17 2012

CROSSREFS

Essentially the same as A055841. First differences of A002001.

Sequence in context: A023872 A034557 A231431 * A075674 A245416 A110752

Adjacent sequences:  A002060 A002061 A002062 * A002064 A002065 A002066

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified December 22 09:44 EST 2014. Contains 252339 sequences.