A280390 - OEIS

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A280390

Integers that can be written using their individual decimal digits and the operations + - * / ^ but not the concatenation of their digits.

25, 125, 127, 128, 216, 289, 343, 347, 625, 736, 1285, 1296, 1792, 2048, 2187

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OFFSET

1,1

COMMENTS

A proper subset of A036057.

LINKS

Table of n, a(n) for n=1..15.

EXAMPLE

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.

MATHEMATICA

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 *)

CROSSREFS

Cf. A036057.

Sequence in context: A360640 A172047 A304422 * A225388 A369563 A146945

Adjacent sequences: A280387 A280388 A280389 * A280391 A280392 A280393

KEYWORD

base,nonn

AUTHOR

Erich Friedman and Robert G. Wilson v, Jan 01 2017

STATUS

approved