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A165246
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a(n) = (10^n+53)/9
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1
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7, 17, 117, 1117, 11117, 111117, 1111117, 11111117, 111111117, 1111111117, 11111111117, 111111111117, 1111111111117, 11111111111117, 111111111111117, 1111111111111117, 11111111111111117, 111111111111111117
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OFFSET
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1,1
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COMMENTS
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a(n) are also n-1 units followed by a seven
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LINKS
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Table of n, a(n) for n=1..18.
Markus Tervooren, Factorizations of (1)w7
Index to sequences with linear recurrences with constant coefficients, signature (11,-10).
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FORMULA
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a(n)=9*a(n-1)-8*a(n-2)+2*10^(n-2) [with a(1)=7, a(2)=17] [From Vincenzo Librandi, Aug 02 2010]
a(n)=11*a(n-1)-10*a(n-2). G.f.: -x*(60*x-7)/((x-1)*(10*x-1)). [Colin Barker, Jan 24 2013]
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EXAMPLE
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a(3)=9*17-8*7+2*10=117; a(4)=9*117-8*17+2*10^2=1117 [From Vincenzo Librandi, Aug 02 2010]
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MATHEMATICA
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Table[FromDigits[PadLeft[{7}, n, 1]], {n, 20}] (* From Harvey P. Dale, Oct 17 2011 *)
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CROSSREFS
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Sequence in context: A067185 A205989 A063384 * A118108 A214149 A147643
Adjacent sequences: A165243 A165244 A165245 * A165247 A165248 A165249
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KEYWORD
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easy,nonn
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AUTHOR
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Ivan Panchenko, Sep 10 2009
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STATUS
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approved
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