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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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FORMULA
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a(n) = 9*a(n-1)-8*a(n-2)+2*10^(n-2) for n>2, a(1)=7, a(2)=17. [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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MATHEMATICA
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Table[FromDigits[PadLeft[{7}, n, 1]], {n, 20}] (* Harvey P. Dale, Oct 17 2011 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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