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
Keywords
Examples
10 is a term because phi(10) = 4; 10 mod 4 = 2 and 10^2 mod 4 = 0.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
Select[Range[10^3], Function[k, And[Divisible[#^2, k], ! Divisible[#, k]]]@ EulerPhi@ # &] (* Michael De Vlieger, Jul 21 2016 *)
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PARI
isok(n) = (n % eulerphi(n) != 0) && (n^2 % eulerphi(n) == 0)