A105267 - OEIS

%I #10 May 13 2020 07:04:14

%S 1,2,2,2,2,2,2,2,4,4,4,8,8,16,4,4,8,2,8,24,8,4,16,8,8,4,16,8,8,6,8,16,

%T 64,4,4,8,8,16,16,2,8,8,64,64,8,4,8,32,8,2,8,8,16,64,8,8,32,8,32,2,8,

%U 64,32,16,8,32,8,8,32,16,64,64,8,64,4,4,16,2

%N a(n) = the number of divisors of 33...31, with n 3s.

%C The first seven 33...31 numbers are prime, so those terms are 2. - _Don Reble_, Oct 26 2006

%H Amiram Eldar, <a href="/A105267/b105267.txt">Table of n, a(n) for n = 0..203</a>

%F a(n) = A000005(A033175(n)). - _Amiram Eldar_, May 13 2020

%t a[n_] := DivisorSigma[0, (10^(n + 1) - 7)/3]; Array[a, 30, 0] (* _Amiram Eldar_, May 13 2020 *)

%o (PARI) a(n) = numdiv((10^(n + 1) - 7)/3); \\ _Michel Marcus_, May 13 2020

%Y Cf. A000005, A051200, A033175, A104484.

%K nonn

%O 0,2

%A _Parthasarathy Nambi_, Apr 29 2005

%E More terms from _Don Reble_, Oct 26 2006