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A138471
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Number of numbers less than n having the same sum of digits.
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7
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 3, 3, 3, 3, 3, 3, 3, 2, 1, 0, 4, 4, 4, 4, 4, 4, 3, 2, 1, 0, 5, 5, 5, 5, 5, 4, 3, 2, 1, 0, 6, 6, 6, 6, 5, 4, 3, 2, 1, 0, 7, 7, 7, 6, 5, 4, 3, 2, 1, 0, 8, 8, 7, 6, 5, 4, 3, 2, 1, 0, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 2, 3, 4, 5, 6
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OFFSET
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0,21
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COMMENTS
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LINKS
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EXAMPLE
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a(42)=#{6,15,24,33}=4.
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MAPLE
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N:= 1000: # to get a(0) to a(N)
C:= Vector(9*(1+ilog10(N))):
A[0]:= 0:
for n from 1 to N do
s:= convert(convert(n, base, 10), `+`);
A[n]:= C[s];
C[s]:= C[s]+1;
od:
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MATHEMATICA
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Module[{nn=110, sd}, sd=Total[IntegerDigits[#]]&/@Range[nn]; Join[{0}, Table[ Count[Take[sd, i-1], sd[[i]]], {i, nn}]]] (* Harvey P. Dale, Aug 14 2013 *)
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PROG
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(PARI) a(n) = my(sdn=sumdigits(n)); sum(k=1, n-1, sumdigits(k) == sdn); \\ Michel Marcus, May 26 2017
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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