A136034 a(n) = smallest number k such that number of distinct prime factors of 2^k-1 is exactly n.

1, 2, 4, 8, 12, 20, 24, 40, 36, 48, 88, 60, 72, 150, 132, 120, 156, 144, 200, 204, 210, 180, 324, 476, 288, 300, 432, 396, 480, 360, 468, 576, 700, 504, 420, 648, 540, 660, 792, 720

Offset

0,2

Comments

First occurrence of n in A046800.

Links

Table of n, a(n) for n=0..39.

Mathematica

With[{pn1=PrimeNu[2^Range[800]-1]}, Table[Position[pn1, n, 1, 1], {n, 0, 40}]]//Flatten (* Harvey P. Dale, Jan 10 2025 *)

Prog

(PARI) a(n) = my(k=1); while (omega(2^k-1) != n, k++); k; \\ Michel Marcus, Jan 09 2023

Crossrefs

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

Sequence in context: A206350 A127405 A344932 * A243112 A230127 A059793

Adjacent sequences: A136031 A136032 A136033 * A136035 A136036 A136037

Keyword

nonn,more,changed

Author

Artur Jasinski, Dec 11 2007

Extensions

More terms from Julián Aguirre, Feb 04 2013

a(31)-a(39) from Chai Wah Wu, Oct 03 2019

a(0) = 1 inserted by Michel Marcus, Jan 09 2023

Status

approved