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A275245 Numbers n such that phi(n) divides n^2 while phi(n) does not divide n. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..52.

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. 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

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Last modified May 20 03:10 EDT 2019. Contains 323412 sequences. (Running on oeis4.)