A046799 - OEIS

%I #44 Jul 25 2023 19:53:49

%S 1,1,1,1,1,2,2,2,1,2,2,2,2,2,3,3,1,2,4,2,2,3,3,2,3,4,4,3,2,3,5,2,2,4,

%T 4,5,4,3,4,3,2,3,6,2,3,5,5,3,3,3,5,5,3,3,6,5,3,4,3,4,4,2,5,5,2,6,6,3,

%U 3,4,6,3,5,3,5,6,4,6,9,2,3,6,5,6,5,4,5,4,4,4,10,6,2,4,4,5,3,5,6,7,6,2,9,3,2

%N Number of distinct prime factors of 2^n+1.

%C The length of row n in A060444.

%H Max Alekseyev, <a href="/A046799/b046799.txt">Table of n, a(n) for n = 0..1122</a> (terms 0..500 from T. D. Noe; terms 501..1062 from Amiram Eldar)

%F a(n) = A001221(A000051(n)). - _Amiram Eldar_, Oct 04 2019

%e For n=7, 129 = 3.43 has 2 prime factors, so a(7) = 2.

%t PrimeNu[1 + 2^#] & /@ Range[0, 104] (* _Jayanta Basu_, Jun 29 2013 *)

%o (PARI) a(n) = omega(2^n+1); \\ _Michel Marcus_, Mar 25 2017

%Y Cf. A000051, A001221, A060444, A086257 (number of primitive prime factors).

%K nonn

%O 0,6

%A _Labos Elemer_