%I #21 Jan 07 2024 13:33:19

%S 1,2,2,3,3,4,3,4,4,5,4,6,3,6,6,5,3,8,3,7,6,7,4,9,7,7,6,8,6,11,3,7,8,7,

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

%U 11,9,9,14,5,10,8,15,6,17,6,10,13,11,10,16,5

%N Number of distinct prime divisors of 4^n - 1.

%H Max Alekseyev, <a href="/A366604/b366604.txt">Table of n, a(n) for n = 1..1122</a>

%F a(n) = omega(4^n-1) = A001221(A024036(n)).

%F a(n) = A046800(2*n) = A046799(n) + A046800(n). - _Max Alekseyev_, Jan 07 2024

%t PrimeNu[4^Range[100]-1] (* _Paolo Xausa_, Oct 14 2023 *)

%o (PARI) for(n = 1, 100, print1(omega(4^n - 1), ", "))

%o (Python)

%o from sympy import primenu

%o def A366604(n): return primenu((1<<(n<<1))-1) # _Chai Wah Wu_, Oct 15 2023

%Y Cf. A024036, A001221, A057957, A133801, A366602, A366603.

%Y Cf. A046800, A133801, A366611, A366620, A366632, A366651, A366660, A102347, A366681, A366707.

%K nonn

%O 1,2

%A _Sean A. Irvine_, Oct 14 2023