A366604 - OEIS

A366604

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

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

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OFFSET

1,2

LINKS

Max Alekseyev, Table of n, a(n) for n = 1..1122

FORMULA

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

a(n) = A046800(2*n) = A046799(n) + A046800(n). - Max Alekseyev, Jan 07 2024

MATHEMATICA

PrimeNu[4^Range[100]-1] (* Paolo Xausa, Oct 14 2023 *)

PROG

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