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 A038821 #21 Apr 03 2023 10:36:09
%S A038821 37607912018,73301896139,108340298703,142966208126,177291661649,
%T A038821 211381427039,245277688804,279010070811,312600354108,346065536839,
%U A038821 379418886337,412671294782,445831610611,478907544860,511905471132
%N A038821 Number of primes less than n*10^12.
%H A038821 Robert G. Wilson v, <a href="/A038821/b038821.txt">Table of n, a(n) for n = 1..10000</a>
%H A038821 Thomas R. Nicely, <a href="https://faculty.lynchburg.edu/~nicely/index.html">Some Results of Computational Research in Prime Numbers</a> [See local copy in A007053]
%H A038821 Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/primes.html">Tables of values of pi(x) and of pi2(x)</a>
%H A038821 Andrew R. Booker, <a href="https://t5k.org/nthprime/">The Nth Prime Page</a>
%t A038821 Table[ PrimePi[ n*10^12 ], {n, 1, 15}]
%o A038821 (PARI) a(n)=primepi(10^12*n) \\ _Charles R Greathouse IV_, Apr 29 2015
%Y A038821 Cf. A038801, A028505, A038812, A038813, A038814, A038815, A038816, A038817, A038818, A038819, A038820, A080122, A080123, A080124, A080125, A080126, A080127, A080128, A080129.
%K A038821 nonn
%O A038821 1,1
%A A038821 _Jeff Burch_
%E A038821 Edited, corrected and extended by _Robert G. Wilson v_, Jan 29 2003