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 A073513 #11 Oct 28 2021 12:59:31
%S A073513 1,3,17,131,1055,8615,72951,633932,5602768,50193913,454577490,
%T A073513 4153943134,38243708524,354330372215,3300752009165,30892997367352,
%U A073513 290332329192655,2738477783884855,25913537508233527,245923809778144431,2339944887042508496,22316931815316988517
%N A073513 Number of primes less than 10^n with initial digit 5.
%H A073513 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 A073513 Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/primes.html">Tables of values of pi(x) and of pi2(x)</a>
%e A073513 a(2)=3 because there are 3 primes up to 10^2 whose initial digit is 5 (namely 5, 53 and 59).
%t A073513 f[n_] := f[n] = PrimePi[6*10^n] - PrimePi[5*10^n] + f[n - 1]; f[0] = 1; Table[ f[n], {n, 0, 13}]
%Y A073513 Cf. A073509 to A073517, their sum is A006880.
%Y A073513 For primes with initial digit d (1 <= d <= 9) see A045707, A045708, A045709, A045710, A045711, A045712, A045713, A045714, A045715; A073517, A073516, A073515, A073514, A073513, A073512, A073511, A073510, A073509
%K A073513 base,hard,nonn
%O A073513 1,2
%A A073513 _Shyam Sunder Gupta_, Aug 14 2002
%E A073513 Edited and extended by _Robert G. Wilson v_, Aug 29 2002
%E A073513 a(20)-a(22) added by _David Baugh_, Mar 22 2015