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Number of primes in the interval [4n, 5n].
8

%I #13 Jul 08 2017 12:16:15

%S 1,0,1,2,1,1,2,1,3,3,2,2,3,3,4,4,4,4,3,3,4,6,6,6,5,4,4,5,4,5,6,6,6,7,

%T 6,7,8,6,8,9,8,7,8,7,7,8,9,9,9,7,8,9,9,10,11,11,12,11,11,10,9,10,11,

%U 12,11,10,11,10,10,11,10,11,11,11,12

%N Number of primes in the interval [4n, 5n].

%H FUNG Cheok Yin, <a href="/A289495/b289495.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) a(n) = primepi(5*n) - primepi(4*n); \\ _Michel Marcus_, Jul 08 2017

%Y Cf. A035250, A289493, A289494, A289496, A289497, A289498, A289499, A289500.

%K nonn,easy

%O 1,4

%A _FUNG Cheok Yin_, Jul 07 2017