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A046801 Number of divisors of 2^n-1. 7
1, 2, 2, 4, 2, 6, 2, 8, 4, 8, 4, 24, 2, 8, 8, 16, 2, 32, 2, 48, 12, 16, 4, 96, 8, 8, 8, 64, 8, 96, 2, 32, 16, 8, 16, 512, 4, 8, 16, 192, 4, 144, 8, 128, 64, 16, 8, 768, 4, 128, 32, 128, 8, 160, 64, 256, 16, 64, 4, 4608, 2, 8, 96, 128, 8, 384, 4, 128, 16, 512, 8, 8192, 8, 32, 128 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(0) cannot be defined because 0's divisors are an infinite set (every number is a divisor of 0.)

LINKS

T. D. Noe, Table of n, a(n) for n = 1..500 (using data from A001265)

EXAMPLE

a(120) = 73728 since 2^120-1 has that many divisors.

MATHEMATICA

Table[DivisorSigma[0, 2^n - 1], {n, 120}] (* Michael De Vlieger, Mar 26 2015 *)

PROG

(PARI) a(n) = numdiv(2^n-1); \\ Michel Marcus, Dec 15 2013

(MAGMA) [DivisorSigma(0, 2^n - 1): n in [1..100]]; // Vincenzo Librandi, Mar 27 2015

CROSSREFS

Cf. A000043 (n such that a(n) = 2), A000225 (2^n-1).

Sequence in context: A067824 A107067 A320389 * A316437 A137502 A318885

Adjacent sequences:  A046798 A046799 A046800 * A046802 A046803 A046804

KEYWORD

nonn

AUTHOR

Labos Elemer

EXTENSIONS

Typo in example fixed by Reinhard Zumkeller, May 15 2010

a(0) removed by J. Lowell, Mar 26 2015

STATUS

approved

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Last modified February 15 22:28 EST 2019. Contains 320138 sequences. (Running on oeis4.)