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 A231593 #14 Jun 16 2019 13:31:12
%S A231593 0,3,34,360,3772,39006,397474,4022501,40604951,408986159,4113511677,
%T A231593 41331763006,414971464358,4163826451096
%N A231593 Total number of 4's digits in primes less than 10^n.
%e A231593 a(2)=3, since there are 3 4's in primes less than 100. Namely: 41, 43, 47.
%t A231593 Table[Count[IntegerDigits[Prime[Range[PrimePi[10^n - 1]]]], 4, 2], {n, 7}] (* _Robert Price_, Jun 16 2019 *)
%Y A231593 Cf. A231411, A231590-A231598, A119290, A119291-A119300.
%K A231593 nonn,base,more
%O A231593 1,2
%A A231593 _Robert Price_, Nov 11 2013
%E A231593 a(14) from _Giovanni Resta_, Jul 20 2015