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%I #11 Feb 15 2014 08:54:14
%S 3,4,5,5,6,6,7,7,8,9,10,10,11,10,12,12,13,14,14,14,15,16,16,16,17,18,
%T 20,21,21,20,20,20,21,22,23,23,24,24,25,25,26,26,27,26,28,28,28,29,30,
%U 31,31,31,32,31,31,32,34,35,35,36,36,35,36,37,37,38,39,39,40,41,42,41
%N Number of primes between n and 4n+1.
%F a(n) = A000720(4*n+1) - A000720(n-1). - _Michel Marcus_, Sep 28 2013
%e a(5)=6 because between 5 and 21 there are 6 primes: 5, 7, 11, 13, 17 and 19.
%p with(numtheory); A037038:=n->pi(4*n + 1) - pi(n - 1); seq(A037038(n), 1..100); # _Wesley Ivan Hurt_, Feb 14 2014
%t Table[PrimePi[4 n + 1] - PrimePi[n - 1], {n, 1, 100}] (* _Wesley Ivan Hurt_, Feb 14 2014 *)
%o (PARI) a(n) = primepi(4*n+1) - 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_
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