A289493 Number of primes in the interval [2n, 3n].

2, 1, 1, 1, 2, 2, 2, 3, 2, 2, 3, 2, 3, 4, 4, 4, 4, 5, 4, 5, 5, 4, 5, 5, 6, 6, 6, 7, 7, 7, 6, 6, 7, 7, 8, 8, 8, 9, 9, 8, 8, 7, 8, 9, 8, 9, 10, 10, 9, 10, 10, 9, 10, 9, 9, 10, 9, 10, 10, 11, 12, 12, 12, 12, 13, 13, 14, 14, 13, 12, 13, 13, 13, 13, 13, 13, 14, 15, 14, 15

Offset: 1

Author

FUNG Cheok Yin, Jul 07 2017

Keywords

• nonn

Links

• FUNG Cheok Yin, Table of n, a(n) for n = 1..10000
• Mohamed El Bachraoui, Primes in the interval [2n, 3n] (2006)
• FUNG Cheok Yin, C++ program

Crossrefs

Cf. A035250, A289494, A289495, A289496, A289497, A289498, A289499, A289500.

Cf. A000720 (PrimePi), A101985 (numbers occurring here exactly once).

Programs

PARI

A289493(n)=primepi(3*n)-if(n>1,primepi(2*n)) \\ M. F. Hasler, Sep 29 2019

Formula

a(n) = A000720(3n) - A000720(2n), for n > 1. - M. F. Hasler, Sep 29 2019