OFFSET
1,1
COMMENTS
If k > 1, then k*phi(k) is not a perfect square. If p is prime, then (p-1)*phi(p) is a perfect square.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
MATHEMATICA
Select[Range[140000], IntegerQ[Sqrt[EulerPhi[#](#+1)]]&] (* Harvey P. Dale, Jan 21 2013 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Apr 27 2002
STATUS
approved