%I #36 Jul 25 2023 19:57:06

%S 1,2,3,3,3,5,3,4,6,6,4,7,3,6,7,5,3,10,3,8,8,7,4,10,7,7,9,8,6,13,3,7,9,

%T 7,9,14,5,7,8,10,5,14,5,10,13,9,6,13,5,14,11,10,6,15,12,11,9,9,6,17,3,

%U 8,14,9,9,15,5,11,9,16,6,19,6,10,14,11,10,18,5,13,16,10,8,19,7,10,11

%N Number of prime factors of 4^n - 1 (counted with multiplicity).

%H Max Alekseyev, <a href="/A057957/b057957.txt">Table of n, a(n) for n = 1..1122</a> (first 603 terms from Amiram Eldar)

%H S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a>

%F Mobius transform of A085029. - _T. D. Noe_, Jun 19 2003

%F a(n) = A001222(A024036(n)) = A046051(2*n). - _Amiram Eldar_, Feb 01 2020

%t PrimeOmega/@(4^Range[90]-1) (* _Harvey P. Dale_, Dec 31 2018 *)

%Y bigomega(b^n-1): A057951 (b=10), A057952 (b=9), A057953 (b=8), A057954 (b=7), A057955 (b=6), A057956 (b=5), this sequence (b=4), A057958 (b=3), A046051 (b=2).

%Y Cf. A001222, A024036, A054992, A085029, A274906.

%K nonn

%O 1,2

%A _Patrick De Geest_, Nov 15 2000