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 A304484 #13 Sep 08 2022 08:46:21 %S A304484 0,0,2,3,6,8,15,15,18,21,28,32,40,40,45,50,60,60,77,77,84,91,104,112, %T A304484 112,112,120,120,135,144,170,170,170,180,180,190,220,220,220,231,252, %U A304484 264,286,286,299,299,322,322,336,336,350,364,390,405,420,420,435,435,464,464 %N A304484 a(n) = A033270(n)*A033270(2n), where A033270 counts the odd primes. %H A304484 Jason Kimberley, <a href="/A304484/b304484.txt">Table of n, a(n) for n = 1..10000</a> %t A304484 Array[(PrimePi@ # - Boole[# > 1]) (PrimePi[2 #] - Boole[2 # > 1]) &, 60] (* _Michael De Vlieger_, May 27 2018 *) %o A304484 (Magma) A033270:=func<n|n le 1 select 0 else #PrimesUpTo(n)-1>; A:=[A033270(n):n in[1..120]]; [A[n]*A[2*n]:n in[1..#A div 2]]; %o A304484 (PARI) a033270(n) = max(primepi(n)-1, 0); %o A304484 a(n) = a033270(n)*a033270(2*n); %Y A304484 Cf. A304483 = A000720(n)*A000720(2n). %K A304484 nonn,easy %O A304484 1,3 %A A304484 _Jason Kimberley_, May 15 2018