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A307629
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Let decimal expansion of n be d_1 d_2 ... d_k; a(n) = Sum_{i=1..k-1} Sum_{j=i+1..k} (d_i + d_j).
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2
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 2, 4, 6
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OFFSET
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0,12
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COMMENTS
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More than the usual number of terms are shown in order to distinguish this from related sequences.
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LINKS
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FORMULA
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EXAMPLE
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For n<10 there is only one decimal digit so a(n)=0.
a(102) = 1+0 + 1+2 + 0+2 = 6.
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MAPLE
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a:= n-> (d-> (nops(d)-1)*add(i, i=d))(convert(n, base, 10)):
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MATHEMATICA
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Array[Total@ Flatten@ Subsets[IntegerDigits@ #, {2}] &, 103, 0] (* Michael De Vlieger, Apr 19 2019 *)
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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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