A105267 a(n) = the number of divisors of 33...31, with n 3s.

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, 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, 64, 32, 16, 8, 32, 8, 8, 32, 16, 64, 64, 8, 64, 4, 4, 16, 2

Offset: 0

Author

Parthasarathy Nambi, Apr 29 2005

Keywords

• nonn

Comments

The first seven 33...31 numbers are prime, so those terms are 2. - Don Reble, Oct 26 2006

Links

• Amiram Eldar, Table of n, a(n) for n = 0..203

Crossrefs

Cf. A000005, A051200, A033175, A104484.

Programs

Mathematica

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

PARI

a(n) = numdiv((10^(n + 1) - 7)/3); \\ Michel Marcus, May 13 2020

Formula

a(n) = A000005(A033175(n)). - Amiram Eldar, May 13 2020

Extensions

More terms from Don Reble, Oct 26 2006