OFFSET
1,2
COMMENTS
The squarefree numbers are a subset of this sequence.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
MATHEMATICA
ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] cor[x_] := Apply[Times, ba[x]] g1[x_] := GCD[DivisorSigma[1, x], EulerPhi[x]] g2[x_] := GCD[DivisorSigma[1, cor[x]], EulerPhi[cor[x]]] Do[s1=g1[n]; s2=g2[n]; If[Equal[s2, s1], Print[n]], {n, 1, 256}]
PROG
(PARI) isok(n) = my(c=core(n)); gcd(sigma(n), eulerphi(n)) == gcd(sigma(c), eulerphi(c)); \\ Michel Marcus, Jul 30 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Oct 17 2002
STATUS
approved