A037037 Number of primes between n and 3n.

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, 14, 14, 13, 14, 15, 16, 17, 18, 18, 18, 18, 18, 17, 18, 18, 18, 19, 20, 19, 19, 20, 21, 21, 22, 21, 22, 23, 23, 24, 24, 24, 25, 24, 24, 25, 26, 27, 28, 27, 27, 27, 28, 27, 27, 26, 27, 28

Offset

1,1

Links

John Cerkan, Table of n, a(n) for n = 1..10000

Formula

a(n) = A000720(3n) - A000720(n-1). - Wesley Ivan Hurt, Jun 15 2013

Example

For example a(5)=4 because between 5 and 15 there are 4 primes: 5, 7, 11 and 13.

Mathematica

Array[Count[Range[#, 3 #], k_ /; PrimeQ@ k] &, 76] (* Michael De Vlieger, Mar 20 2017 *)

Prog

(PARI) a(n) = primepi(3*n) - primepi(n-1); \\ Michel Marcus, Sep 28 2013

Crossrefs

Cf. A014085.

Sequence in context: A293137 A087823 A230418 * A156262 A218447 A305845

Adjacent sequences: A037034 A037035 A037036 * A037038 A037039 A037040

Keyword

nonn

Author

Felice Russo

Extensions

More terms from Erich Friedman

Status

approved