A069953 Composite n such that (n-1)*phi(n) is a perfect square.

10, 28, 51, 170, 243, 246, 946, 1128, 1281, 1353, 1695, 2431, 4336, 4411, 4625, 4803, 7501, 7936, 8625, 11914, 12545, 13255, 15051, 16385, 24643, 27870, 29404, 31828, 33490, 36751, 39676, 47046, 52801, 53291, 55471, 58807, 66249, 72076, 74061, 81676, 90775

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

Sequence in context: A088407 A267012 A273195 * A113746 A177720 A117464

Adjacent sequences: A069950 A069951 A069952 * A069954 A069955 A069956

Keyword

easy,nonn

Author

Benoit Cloitre, Apr 27 2002

Status

approved