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 A329174 #25 Nov 16 2019 02:15:32
%S A329174 1,4,20,74,154,499,510,4411,6984,33836,61282,709339,1570651
%N A329174 a(n) is the least positive exponent k such that the decimal expansion of 7^k contains n consecutive zeros.
%e A329174 7^20 = 79792266297612001 is the first power of 7 that has 2 consecutive zeros, so a(2) = 20.
%e A329174 7^74 = 344552147465294110719732986332367243247925798357929806000836849 is the first power of 7 that has 3 consecutive zeros, so a(3) = 74.
%t A329174 Print[1]; zero = {}; Do[zero = zero <> "0"; k = 1; While[StringPosition[ToString[7^k], zero] == {}, k++]; Print[k];, {n, 1, 10}]
%Y A329174 Cf. A006889 (2^k), A195269 (3^k), A329172 (5^k).
%K A329174 nonn,base,more,hard
%O A329174 0,2
%A A329174 _Vaclav Kotesovec_, Nov 07 2019
%E A329174 a(12) from _Chai Wah Wu_, Nov 13 2019