OFFSET
1,2
COMMENTS
Numbers n such that sigma(n) divides primorial(n), that is, A002110(n) mod A000203(n) = 0. - Gary Detlefs, May 02 2012
LINKS
Harry J. Smith, Table of n, a(n) for n = 1..1000
FORMULA
Solutions to |mu(sigma(x))| = 1.
EXAMPLE
For m=100, sigma(100) = 217 = 7*31.
MATHEMATICA
Select[Range@ 300, SquareFreeQ@ DivisorSigma[1, #] &] (* or *)
Select[Range@ 300, Abs@ MoebiusMu@ DivisorSigma[1, #] == 1 &] (* Michael De Vlieger, Mar 18 2017 *)
PROG
(PARI) { n=0; for (m = 1, 10^9, if (abs(moebius(sigma(m)))==1, write("b065300.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 15 2009
(PARI) for(n=1, 300, if(issquarefree(sigma(n)), print1(n, ", "))) \\ Indranil Ghosh, Mar 19 2017
(Python)
from sympy import mobius, divisor_sigma
from sympy.ntheory.factor_ import core
[n for n in range(1, 301) if abs(mobius(divisor_sigma(n, 1))) == 1] #* or *#
[n for n in range(1, 301) if core(divisor_sigma(n, 1)) == divisor_sigma(n, 1)] # Indranil Ghosh, Mar 19 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Oct 29 2001
STATUS
approved