A069068 Composite numbers k+1 such that k*phi(k+1) is a perfect square.

9, 27, 50, 169, 242, 245, 945, 1127, 1280, 1352, 1694, 2430, 4335, 4410, 4624, 4802, 7500, 7935, 8624, 11913, 12544, 13254, 15050, 16384, 24642, 27869, 29403, 31827, 33489, 36750, 39675, 47045, 52800, 53290, 55470, 58806, 66248, 72075, 74060, 81675, 90774, 90972

Offset

1,1

Comments

Trivially if k+1 is prime k*phi(k+1) = k^2. If k>1 k*phi(k) is never a perfect square.

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Mathematica

Select[Range[60000], !PrimeQ[ #+1] && IntegerQ[Sqrt[ # EulerPhi[1+# ]]]&] (* T. D. Noe, Nov 01 2006 *)

Crossrefs

Cf. A000010, A000290.

Sequence in context: A020208 A020306 A330680 * A051412 A027468 A158926

Adjacent sequences: A069065 A069066 A069067 * A069069 A069070 A069071

Keyword

easy,nonn

Author

Benoit Cloitre, Apr 05 2002

Extensions

Corrected by T. D. Noe, Nov 01 2006

More terms from Amiram Eldar, Apr 29 2022

Status

approved