OFFSET
1,2
COMMENTS
REFERENCES
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..300
W. Sierpinski, Number Of Divisors And Their Sum
Wikipedia, Euler's totient function
EXAMPLE
for n=3,phi(3) = 2, tau(2)=2, rad(3)=3 and phi(3) = 2 for n=18900,phi(18900) =4320,tau(4320)= 48, rad(18900)=210, and phi(210) = 48
MAPLE
with(numtheory):for n from 1 to 20000 do: t1:= ifactors(n)[2] : t2 :=mul(t1[i][1], i=1..nops(t1)): if tau(phi(n))= phi(t2)then print (n): else fi: od :
MATHEMATICA
Select[Range[17000], DivisorSigma[0, EulerPhi[#]]==EulerPhi[Times @@ FactorInteger[ #][[All, 1]]]&] (* Harvey P. Dale, Oct 24 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Feb 23 2010; corrected Feb 27 2010
EXTENSIONS
Corrected by Harvey P. Dale, Oct 24 2017
STATUS
approved