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A133195
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Smallest number whose sum of digits is 3n.
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1
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0, 3, 6, 9, 39, 69, 99, 399, 699, 999, 3999, 6999, 9999, 39999, 69999, 99999, 399999, 699999, 999999, 3999999, 6999999, 9999999, 39999999, 69999999, 99999999, 399999999, 699999999, 999999999, 3999999999, 6999999999, 9999999999, 39999999999, 69999999999
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = a(n-1)+10*a(n-3)-10*a(n-4). G.f.: 3*x*(x^2+x+1) / ((x-1)*(10*x^3-1)). [Colin Barker, Feb 01 2013]
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MATHEMATICA
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LinearRecurrence[{1, 0, 10, -10}, {0, 3, 6, 9}, 40] (* Harvey P. Dale, Oct 01 2018 *)
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PROG
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(Python)
def a(n): q, r = divmod(3*n, 9); return int(str(r) + "9"*q)
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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