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 A289493 #20 Sep 30 2019 01:58:09 %S A289493 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, %T A289493 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, %U A289493 12,12,13,13,14,14,13,12,13,13,13,13,13,13,14,15,14,15 %N A289493 Number of primes in the interval [2n, 3n]. %H A289493 FUNG Cheok Yin, <a href="/A289493/b289493.txt">Table of n, a(n) for n = 1..10000</a> %H A289493 Mohamed El Bachraoui, <a href="http://www.researchgate.net/publication/267076371_Primes_in_the_interval_2n3n">Primes in the interval [2n, 3n]</a> (2006) %H A289493 FUNG Cheok Yin, <a href="/A289493/a289493.cpp.txt">C++ program</a> %F A289493 a(n) = A000720(3n) - A000720(2n), for n > 1. - _M. F. Hasler_, Sep 29 2019 %o A289493 (PARI) A289493(n)=primepi(3*n)-if(n>1,primepi(2*n)) \\ _M. F. Hasler_, Sep 29 2019 %Y A289493 Cf. A035250, A289494, A289495, A289496, A289497, A289498, A289499, A289500. %Y A289493 Cf. A000720 (PrimePi), A101985 (numbers occurring here exactly once). %K A289493 nonn %O A289493 1,1 %A A289493 _FUNG Cheok Yin_, Jul 07 2017