OFFSET
1,12
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
MATHEMATICA
Table[GCD[DivisorSigma[1, n], EulerPhi@ n] - GCD[DivisorSigma[1, #], EulerPhi@ #] &[Times @@ FactorInteger[n][[All, 1]]], {n, 120}] (* Michael De Vlieger, Feb 19 2017 *)
PROG
(PARI) rad(f)=for(i=1, #f~, f[i, 2]=1); f
g(f)=gcd(sigma(f), eulerphi(f))
a(n)=my(f=factor(n), k=rad(f)); g(f)-g(k) \\ Charles R Greathouse IV, Dec 09 2013
CROSSREFS
KEYWORD
sign
AUTHOR
Labos Elemer, Dec 04 2001
STATUS
approved