This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A289495 #13 Jul 08 2017 12:16:15 %S A289495 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 A289495 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 A289495 12,11,10,11,10,10,11,10,11,11,11,12 %N A289495 Number of primes in the interval [4n, 5n]. %H A289495 FUNG Cheok Yin, <a href="/A289495/b289495.txt">Table of n, a(n) for n = 1..10000</a> %o A289495 (PARI) a(n) = primepi(5*n) - primepi(4*n); \\ _Michel Marcus_, Jul 08 2017 %Y A289495 Cf. A035250, A289493, A289494, A289496, A289497, A289498, A289499, A289500. %K A289495 nonn,easy %O A289495 1,4 %A A289495 _FUNG Cheok Yin_, Jul 07 2017