OFFSET
1,1
COMMENTS
Warning: It is only conjectured that there are no solutions for n such that a(n) = 0. The search for solutions tested all m <= 10^10 for these n.
For odd remainders a(n) is a square or twice a square. See A028982, except terms 1 and 2.
All zeros corresponding to odd terms a(n) with n < 64 confirmed up to m <= 10^24. - Giovanni Resta, Apr 02 2020
EXAMPLE
For n=4: a(4)=24 since sigma(24)=60, phi(24)=8 and Mod(60, 8)=4.
MATHEMATICA
f[x_] := Mod[DivisorSigma[1, x], EulerPhi[x]]; t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 10000000000}]; t
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
Labos Elemer, Jul 12 2002
EXTENSIONS
Name corrected by Sean A. Irvine, Oct 30 2024
STATUS
approved