OFFSET
1,1
COMMENTS
If k>1 k*phi(k) is not a perfect square. Trivially, if p is prime (p-1)*phi(p) is a perfect square.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
MATHEMATICA
psQ[n_]:=CompositeQ[n]&&IntegerQ[Sqrt[(n-1)EulerPhi[n]]]; Select[ Range[ 100000], psQ] (* Harvey P. Dale, Nov 08 2017 *)
PROG
(PARI) for(n=2, 120000, if(frac(sqrt((n-1+isprime(n))*eulerphi(n)))==0, print1(n, ", ")))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Apr 27 2002
STATUS
approved