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 A166678 #21 Aug 15 2022 08:34:51
%S A166678 2,2,3,6,14,34,110,384,1540,7019,34501,183439,1045196,6164423,38285946
%N A166678 a(n) = pi((sqrt(P(n))+1)^2) - pi(P(n)), where pi(n) = number of primes <= n and P(n) = n-th primorial.
%C A166678 Conjecture: pi((sqrt(P(n))+1)^2) - pi(P(n)) >= n.
%t A166678 a[n_] := Product[Prime[k], {k, 1, n}]; Table[PrimePi[(Sqrt[a[n]] + 1)^2] - PrimePi[a[n]], {n, 1, 12}] (* _G. C. Greubel_, May 22 2016 *)
%o A166678 (PARI) a(n) = my(P=vecprod(primes(n))); primepi((sqrt(P)+1)^2) - primepi(P); \\ _Michel Marcus_, Aug 15 2022
%Y A166678 Cf. A000720 (pi), A002110 (primorials), A000849 (pi(primorials)).
%K A166678 nonn,more,less
%O A166678 1,1
%A A166678 _Daniel Tisdale_, Oct 18 2009, Oct 23 2009
%E A166678 a(13)-a(15) from _Ray Chandler_, May 10 2010
%E A166678 Name edited by _Michel Marcus_, Aug 15 2022