OFFSET
1,1
COMMENTS
In the link, P. Pollack and C. Pomerance "show that almost all squares are missing from the range of Euler's phi-function".
Except for m=1 and m=2, phi(m) is always even, so, the odd numbers >= 3 are not included in the data for clarity.
Includes 2*p if p is a prime not in A052291. - Robert Israel, Apr 10 2019
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
P. Pollack and C. Pomerance, Square values of Euler's function, preprint (2013); Bulletin of the London Mathematical Society, Volume 46, Issue 2, 1 April 2014, Pages 403-414.
EXAMPLE
phi(489) = 18^2, phi(401) = 20^2, phi(577) = 24^2, phi(677) = 26^2, but there is no integer m such that phi(m) = 22^2 = 484.
MAPLE
select(t -> numtheory:-invphi(t^2)=[], [seq(i, i=2..400, 2)]); # Robert Israel, Apr 10 2019
PROG
(PARI) isok(n) = !(n%2) && !istotient(n^2); \\ Michel Marcus, Mar 15 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Bernard Schott, Mar 15 2019
STATUS
approved