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A280390
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Integers that can be written using their individual decimal digits and the operations + - * / ^ but not the concatenation of their digits.
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0
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25, 125, 127, 128, 216, 289, 343, 347, 625, 736, 1285, 1296, 1792, 2048, 2187
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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125 is in the sequence since 5^(1+2) but 121 is not in the sequence. We do not accept 11^2 since 11 is the concatenation of two digits.
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MATHEMATICA
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ops = {Plus, Subtract, Times, Divide, Power}; fQ[n_] := Length@ Select[ Groupings[ Permutations@ IntegerDigits@ n, ops -> 2], # == n &] > 0; k = 1; lst = {}; While[k < 1001, If[fQ@k, AppendTo[lst, k]]; k++]; lst (* requires Mathematica version 11 or better *)
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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