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A002279
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a(n) = 5*(10^n - 1)/9.
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39
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0, 5, 55, 555, 5555, 55555, 555555, 5555555, 55555555, 555555555, 5555555555, 55555555555, 555555555555, 5555555555555, 55555555555555, 555555555555555, 5555555555555555, 55555555555555555, 555555555555555555, 5555555555555555555, 55555555555555555555, 555555555555555555555
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OFFSET
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0,2
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COMMENTS
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Arithmetic mean of all n-digit odd numbers. E.g., a(2) = arithmetic mean of {11,13,15,...,97,99} = (11+99)/2 = 55. - Amarnath Murthy, Aug 02 2005
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LINKS
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Eric Weisstein's World of Mathematics, Repdigit.
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FORMULA
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a(n) = a(n-1) + 5*10^(n-1) with a(0)=0.
a(n) = 11*a(n-1) - 10*a(n-2) with a(0)=0, a(1)=5. (End)
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MATHEMATICA
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Table[FromDigits[PadRight[{}, n, 5]], {n, 0, 20}] (* Harvey P. Dale, Oct 05 2013 *)
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PROG
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(Python)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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