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 A324278 Exponential untouchable numbers: numbers that are not the sum of aliquot exponential divisors of any number. 2

%I

%S 1,4,8,9,16,20,25,27,28,32,40,44,45,49,52,54,63,64,68,75,76,81,88,92,

%T 96,99,104,108,116,117,121,124,125,128,136,144,147,148,152,153,160,

%U 164,169,171,172,175,176,184,188,189,192,196,200,207,208,212,216,224

%N Exponential untouchable numbers: numbers that are not the sum of aliquot exponential divisors of any number.

%C The terms are conjectural and based on a search for solutions to esigma(x) - x = k for k in the range of the data section and x < 10^12 (esigma(x) - x = A051377(x) - x = A126164(x) is the sum of aliquot exponential divisors of x). - _Amiram Eldar_, Jan 22 2020

%t fun[p_, e_] := DivisorSum[e, p^# &]; esigma = 1; esigma[n_] := esigma[n] = Times @@ fun @@@ FactorInteger[n]; untouchableQ[n_] := Catch[ Do[ If[n == esigma[k]-k, Throw[True]], {k, 0, (n+1)^2}]] === Null; Reap[ Table[ If[ untouchableQ[n], Sow[n]], {n, 1, 130}]][[2, 1]] (* after Jean-François Alcover at A005114 *)

%Y Cf. A051377, A126164, A005114, A063948 (unitary), A324276 (bi-unitary), A324277 (infinitary).

%K nonn

%O 1,2

%A _Amiram Eldar_, Feb 20 2019

%E Data corrected by _Amiram Eldar_, Jan 22 2020

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Last modified April 19 05:26 EDT 2021. Contains 343105 sequences. (Running on oeis4.)