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a(n) = smallest number k such that number of distinct prime factors of 2^k-1 is exactly n.
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%I #17 Jan 09 2023 07:52:27

%S 1,2,4,8,12,20,24,40,36,48,88,60,72,150,132,120,156,144,200,204,210,

%T 180,324,476,288,300,432,396,480,360,468,576,700,504,420,648,540,660,

%U 792,720

%N a(n) = smallest number k such that number of distinct prime factors of 2^k-1 is exactly n.

%C First occurrence of n in A046800.

%o (PARI) a(n) = my(k=1); while (omega(2^k-1) != n, k++); k; \\ _Michel Marcus_, Jan 09 2023

%Y Cf. A000225, A003260, A016047, A046051, A046800, A049479, A088863, A136030, A136031, A136032, A136033.

%K nonn,more

%O 0,2

%A _Artur Jasinski_, Dec 11 2007

%E More terms from _Julián Aguirre_, Feb 04 2013

%E a(31)-a(39) from _Chai Wah Wu_, Oct 03 2019

%E a(0) = 1 inserted by _Michel Marcus_, Jan 09 2023