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A155988
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a(n) = (2*n+1)*9^n.
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7
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1, 27, 405, 5103, 59049, 649539, 6908733, 71744535, 731794257, 7360989291, 73222472421, 721764371007, 7060738412025, 68630377364883, 663426981193869, 6382625094934119, 61149666232110753, 583701359488329915
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graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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LINKS
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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
Index to sequences with linear recurrences with constant coefficients, signature (18,-81).
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FORMULA
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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).
a(n) = A005408(n) * A001019(n).
a(n) = (2n-1) * 3^(2n-1) / 3 = A060851(n) / 3.
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PROG
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(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 */
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CROSSREFS
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Cf. A058962 for the similar (2n+1)4^n.
Cf. A001019, A005408, A060851, A096949, A096950, A154920, A164985, A165132.
Sequence in context: A296853 A036222 A022655 * A096950 A307911 A125484
Adjacent sequences: A155985 A155986 A155987 * A155989 A155990 A155991
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KEYWORD
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nonn,easy
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AUTHOR
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Jaume Oliver Lafont, Feb 01 2009
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STATUS
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approved
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