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%I #27 Mar 07 2021 01:16:34
%S 0,1,2,3,5,6,7,9,10,11,13,14,16,18,19,20,22,24,25,27,28,29,31,32,34,
%T 36,37,39,41,42,43,45,47,48,50,51,52,54,56,57,59,60,62,64,65,67,69,71,
%U 72,74,75,76,78,79,80,82,83,85,87,89,91,93,95,96,98,99,101,103,104,105
%N Number of composites <= 2*n.
%H Harry J. Smith, <a href="/A065896/b065896.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = A065855(2*n). - _Reinhard Zumkeller_, Oct 14 2014
%e a(9) = 10, since 18 is the 10th composite number: 4, 6, 8, 9, 10, 12, 14, 15, 16, 18.
%t Table[2*n-(PrimePi[2*n])-1, {n, 1, 128}]
%o (PARI) { for (n=1, 1000, f=2*n; a=f - primepi(f) - 1; write("b065896.txt", n, " ", a) ) } \\ _Harry J. Smith_, Nov 04 2009
%o (Haskell)
%o a065896 = a065855 . (* 2) -- _Reinhard Zumkeller_, Oct 14 2014
%Y Cf. A002808, A000720, A005843, A065855.
%K nonn
%O 1,3
%A _Labos Elemer_, Nov 28 2001
%E More precise definition from _Michel Marcus_, Mar 07 2021~
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