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%I #18 Mar 21 2017 08:49:51
%S 2,3,3,3,4,4,5,5,5,6,7,6,7,7,8,9,9,9,9,9,10,10,11,11,12,12,13,14,14,
%T 14,14,13,14,15,16,17,18,18,18,18,18,17,18,18,18,19,20,19,19,20,21,21,
%U 22,21,22,23,23,24,24,24,25,24,24,25,26,27,28,27,27,27,28,27,27,26,27,28
%N Number of primes between n and 3n.
%H John Cerkan, <a href="/A037037/b037037.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A000720(3n) - A000720(n-1). - _Wesley Ivan Hurt_, Jun 15 2013
%e For example a(5)=4 because between 5 and 15 there are 4 primes: 5, 7, 11 and 13.
%t Array[Count[Range[#, 3 #], k_ /; PrimeQ@ k] &, 76] (* _Michael De Vlieger_, Mar 20 2017 *)
%o (PARI) a(n) = primepi(3*n) - primepi(n-1); \\ _Michel Marcus_, Sep 28 2013
%Y Cf. A014085.
%K nonn
%O 1,1
%A _Felice Russo_
%E More terms from _Erich Friedman_