OFFSET
1,1
COMMENTS
From Torlach Rush, Jul 03 2018: (Start)
Consider the quotients q(t) = lcm({x: phi(x)=t})/gcd({x: phi(x)=t}).
When the number of solutions is 2, q(t) must be 2. For example invphi(10) = [11, 22], and q(10)=2.
When the number of solutions is 3, the solutions are x1 < x2 < (2 * x1) and the only observed value of q(t) is 12. For example, invphi(44) = [69, 92, 138], and q(44)=12.
When the number of solutions is greater than 3, multiple values of q(t) are observed. (End)
LINKS
Max Alekseyev, PARI scripts for various problems
EXAMPLE
invphi(1) = [1, 2] and lcm(1, 2) / gcd(1, 2) is 2.
MATHEMATICA
Map[LCM[##]/GCD[##] & @@ # &, Take[Values@ KeySort@ PositionIndex@ Array[EulerPhi, 10^6], 50]] (* Michael De Vlieger, Jul 20 2018 *)
PROG
(PARI) lista(nn) = {for (n=1, nn, my(v = invphi(n)); if (#v, print1(lcm(v)/gcd(v), ", ")); ); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Jul 19 2018
STATUS
approved