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Numbers k such that phi(k) is a multiple of 8.
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%I #34 Nov 18 2022 02:42:18

%S 15,16,17,20,24,30,32,34,35,39,40,41,45,48,51,52,55,56,60,64,65,68,70,

%T 72,73,75,78,80,82,84,85,87,88,89,90,91,95,96,97,100,102,104,105,110,

%U 111,112,113,115,116,117,119,120,123,128,130,132,135,136,137,140,143

%N Numbers k such that phi(k) is a multiple of 8.

%F A000010(a(n)) == 0 (mod 8).

%t Select[Range[150], Divisible[EulerPhi[#], 8] &] (* _Amiram Eldar_, Oct 27 2022 *)

%o (Python)

%o from sympy.ntheory import totient

%o def isok(n): return totient(n) % 8 == 0

%o (PARI) isok(k) = Mod(eulerphi(k), 8) == 0; \\ _Michel Marcus_, Oct 27 2022

%Y Cf. A000010 (phi), A053574 (its 2-adic valuation), A037074 (a subsequence).

%Y Totient multiples: A066498 (3), A172019 (4), A066500 (5), A066502 (7), A332512 (12).

%K nonn

%O 1,1

%A _DarĂ­o Clavijo_, Oct 26 2022