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A155988 (2*n+1)*9^n 7
1, 27, 405, 5103, 59049, 649539, 6908733, 71744535, 731794257, 7360989291, 73222472421, 721764371007, 7060738412025, 68630377364883, 663426981193869, 6382625094934119, 61149666232110753, 583701359488329915 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

David H. Bailey, A Compendium of BBP-Type Formulas for Mathematical Constants, page 14. [From Jaume Oliver Lafont, Sep 25 2009]

X. Gourdon and P. Sebah, Collection of formulas for log 2

FORMULA

G.f.: (1+9*x)/(1-9*x)^2

a(0)=1, a(1)=27, a(n)=18*a(n-1)-81*a(n-2) for n>=2.

sum(n>=0, 1/a(n) ) = (3/2)*log(2).

PROG

(PARI) a(n)=(2*n+1)*9^n;

(MAGMA) [(2*n+1)*9^n: n in [0..20]]; // Vincenzo Librandi, Jun 08 2011

(Maxima) makelist((2*n+1)*9^n, n, 0, 20); /* Martin Ettl, Nov 11 2012 */

CROSSREFS

a(n)=A005408(n)*A001019(n). Cf. A096949, A096950, A058962 (2n+1)4^n.

Cf. A154920, A164985, A165132. [From Jaume Oliver Lafont, Sep 25 2009]

Sequence in context: A296853 A036222 A022655 * A096950 A307911 A125484

Adjacent sequences:  A155985 A155986 A155987 * A155989 A155990 A155991

KEYWORD

nonn

AUTHOR

Jaume Oliver Lafont, Feb 01 2009

STATUS

approved

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Last modified October 23 16:46 EDT 2019. Contains 328373 sequences. (Running on oeis4.)