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A136033 a(n) = smallest number k such that number of prime factors of 2^k-1 is exactly n (counted with multiplicity). 1
2, 4, 6, 16, 12, 18, 24, 40, 54, 36, 102, 110, 60, 72, 108, 140, 120, 156, 144, 200, 216, 210, 240, 180, 456, 288, 336, 300, 396, 480, 882, 360, 468, 700 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..34.

MAPLE

N:= 24: # to get a(1) to a(N)

unknown:= N:

for k from 2 while unknown > 0 do

  q:= numtheory:-bigomega(2^k-1);

  if q <= N and not assigned(A[q]) then

     A[q]:= k;

     unknown:= unknown - 1;

  fi

od:

seq(A[i], i=1..N); # Robert Israel, Oct 24 2014

PROG

(PARI) a(n) = {k = 1; while(bigomega(2^k-1) != n, k++); k; } \\ Michel Marcus, Nov 04 2013

CROSSREFS

Cf. A000225, A003260, A016047, A046051, A049479, A088863, A136030, A136031.

Sequence in context: A127679 A049022 A209867 * A343019 A099315 A005179

Adjacent sequences:  A136030 A136031 A136032 * A136034 A136035 A136036

KEYWORD

nonn,more,hard

AUTHOR

Artur Jasinski, Dec 11 2007

EXTENSIONS

a(15)-a(20) from Michel Marcus, Nov 04 2013

a(21)-a(24) from Derek Orr, Oct 23 2014

a(25)-a(34) from Jinyuan Wang, Jun 07 2019

STATUS

approved

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Last modified May 9 02:55 EDT 2021. Contains 343685 sequences. (Running on oeis4.)