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A046798 Number of divisors of 2^n + 1. 6
2, 2, 2, 3, 2, 4, 4, 4, 2, 8, 6, 4, 4, 4, 8, 12, 2, 4, 16, 4, 4, 12, 8, 4, 8, 16, 16, 20, 4, 8, 48, 4, 4, 24, 16, 32, 16, 8, 16, 12, 4, 8, 64, 4, 8, 64, 32, 8, 8, 8, 64, 48, 8, 8, 64, 48, 8, 24, 8, 16, 16, 4, 32, 64, 4, 64, 64, 8, 12, 24, 96, 8, 32, 8, 32, 96, 16, 64, 768, 4, 8, 192, 32, 64 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 0..1062 (terms 0..500 from T. D. Noe, using data from A001269)

FORMULA

a(n) = A000005(A000051(n)). - Michel Marcus, Mar 18 2017

EXAMPLE

a(7)=4, because 2^7 + 1 = 129 has 4 divisors.

MATHEMATICA

A046798[n_IntegerQ]:=DivisorSigma[0, 1+2^n]; (* Enrique Pérez Herrero, Nov 09 2010 *)

DivisorSigma[0, 1 + 2^#] & /@ Range[0, 83] (* Jayanta Basu, Jun 29 2013 *)

Table[DivisorSigma[0, 2^n + 1], {n, 0, 100}] (* Vincenzo Librandi, Feb 05 2018 *)

PROG

(PARI) a(n) = numdiv(2^n+1); \\ Michel Marcus, Mar 18 2017

(Python)

from sympy.ntheory import divisor_count

def A046798(n): return divisor_count(2**n + 1) # Indranil Ghosh, Mar 18 2017

(MAGMA) [NumberOfDivisors(2^n+1): n in [0..100]]; // Vincenzo Librandi, Feb 05 2018

CROSSREFS

Cf. A000005, A000051.

Sequence in context: A121611 A300066 A286545 * A329434 A157231 A258596

Adjacent sequences:  A046795 A046796 A046797 * A046799 A046800 A046801

KEYWORD

nonn

AUTHOR

Labos Elemer

STATUS

approved

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Last modified November 14 22:45 EST 2019. Contains 329135 sequences. (Running on oeis4.)