A275245 Numbers k such that phi(k) divides k^2 while phi(k) does not divide k.

10, 20, 40, 42, 50, 60, 80, 84, 100, 114, 120, 126, 136, 156, 160, 168, 180, 200, 220, 228, 240, 250, 252, 272, 294, 300, 312, 320, 336, 342, 360, 378, 400, 440, 444, 456, 468, 480, 500, 504, 540, 544, 588, 600, 624, 640, 672, 684, 720, 756, 800, 816

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

10 is a term because phi(10) = 4; 10 mod 4 = 2 and 10^2 mod 4 = 0.

Mathematica

Select[Range[10^3], Function[k, And[Divisible[#^2, k], ! Divisible[#, k]]]@ EulerPhi@ # &] (* Michael De Vlieger, Jul 21 2016 *)

Prog

(PARI) isok(n) = (n % eulerphi(n) != 0) && (n^2 % eulerphi(n) == 0)

Crossrefs

Cf. A000010, A007694, A090778.

Sequence in context: A266087 A047881 A172172 * A020953 A033846 A114931

Adjacent sequences: A275242 A275243 A275244 * A275246 A275247 A275248

Keyword

nonn

Author

Altug Alkan, Jul 21 2016

Status

approved