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 A231596 #12 Jun 16 2019 14:00:39
%S A231596 1,9,78,652,6172,58327,560506,5443074,53152746,521422184,5132090751,
%T A231596 50642752951,500714890907,4958432528817
%N A231596 Total number of 7's digits in primes less than 10^n.
%e A231596 a(2)=9, since there are 9 7's in primes less than 100. Namely: 7, 17, 37, 47, 67, 71, 73, 79, 97.
%t A231596 Table[Count[IntegerDigits[Prime[Range[PrimePi[10^n - 1]]]], 7, 2], {n, 7}] (* _Robert Price_, Jun 16 2019 *)
%Y A231596 Cf. A231411, A231590-A231598, A119290, A119291-A119300.
%K A231596 more,nonn,base
%O A231596 1,2
%A A231596 _Robert Price_, Nov 11 2013
%E A231596 a(14) from _Giovanni Resta_, Jul 20 2015