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 A057860 Number of residue classes modulo n which contain only composite numbers. 2

%I

%S 0,0,0,1,0,2,0,3,2,4,0,6,0,6,5,7,0,10,0,10,7,10,0,14,4,12,8,14,0,19,0,

%T 15,11,16,9,22,0,18,13,22,0,27,0,22,19,22,0,30,6,28,17,26,0,34,13,30,

%U 19,28,0,41,0,30,25,31,15,43,0,34,23

%N Number of residue classes modulo n which contain only composite numbers.

%H G. C. Greubel, <a href="/A057860/b057860.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = n - A057859(n) = A051953(n) - A001221(n).

%e a(30) = 19 since 30k+m is always composite if m = 0, 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27 or 28

%t Table[n - EulerPhi[n] - PrimeNu[n], {n, 1, 100}] (* _G. C. Greubel_, May 13 2017 *)

%o (PARI) for(n=1,100, print1(n - eulerphi(n) - omega(n), ", ")) \\ _G. C. Greubel_, May 13 2017

%Y Cf. A057858.

%K nonn,look

%O 1,6

%A _Henry Bottomley_, Sep 08 2000

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Last modified September 19 08:54 EDT 2021. Contains 347556 sequences. (Running on oeis4.)