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A324277 Infinitary untouchable numbers: numbers that are not the sum of aliquot infinitary divisors of any number. 4
2, 3, 4, 5, 38, 68, 80, 128, 158, 164, 188, 192, 206, 212, 224, 278, 290, 308, 326, 368, 380, 398, 416, 432, 458, 518, 530, 536, 542, 548, 578, 584, 600, 626, 632, 692, 702, 710, 752, 758, 770, 782, 788, 818, 822, 836, 852, 872, 896, 902, 926, 938, 968, 998 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..2256 (terms below 30000)

MATHEMATICA

fun[p_, e_] := Module[{b = IntegerDigits[e, 2]}, m = Length[b]; Product[If[b[[j]] > 0, 1 + p^(2^(m - j)), 1], {j, 1, m}]]; isigma[1] = 1; isigma[n_] := isigma[n] = Times @@ (fun @@@ FactorInteger[n]); untouchableQ[n_] := Catch[ Do[ If[n == isigma[k]-k, Throw[True]], {k, 0, (n-1)^2}]] === Null; Reap[ Table[ If[ untouchableQ[n], Sow[n]], {n, 2, 1000}]][[2, 1]] (* after Jean-Fran├žois Alcover at A005114 *)

CROSSREFS

Cf. A049417, A126168, A005114, A063948 (unitary), A324276 (bi-unitary), A324278 (exponential).

Sequence in context: A044907 A252079 A324276 * A261247 A153719 A024637

Adjacent sequences:  A324274 A324275 A324276 * A324278 A324279 A324280

KEYWORD

nonn

AUTHOR

Amiram Eldar, Feb 20 2019

STATUS

approved

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Last modified April 14 10:14 EDT 2021. Contains 342949 sequences. (Running on oeis4.)