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 A333431 #32 Mar 22 2020 10:07:22
%S A333431 0,1,2,3,4,9,24,342,11158,145435633325318659
%N A333431 Numbers k such that k! has a factorial number of decimal digits.
%C A333431 From _Vaclav Kotesovec_, Mar 22 2020: (Start)
%C A333431 a(11) has 1199 digits and a(11)! has 525! digits.
%C A333431 a(12) has 1300 digits and a(12)! has 562! digits.
%C A333431 a(13) has 3733 digits and a(13)! has 1380! digits.
%C A333431 a(14) has 4730 digits and a(14)! has 1693! digits.
%C A333431 a(15), if it exists, must have more than 5732 digits and a(15)! must have more than 2000! digits. (End)
%H A333431 Vaclav Kotesovec, <a href="/A333431/a333431_1.txt">a(11)-a(14)</a>
%e A333431 9 is in the sequence since 9! = 362880 which has 6 decimal digits and 6 = 3!.
%t A333431 f = k = 1; lst = {0}; While[k < 12000, f *= k; If[ MemberQ[{1, 2, 6, 24, 120, 720, 5040, 40320, 362880}, IntegerLength@ f], AppendTo[lst, k]]; k++]; lst
%Y A333431 Cf. A000142, A034886.
%K A333431 nonn,base
%O A333431 1,3
%A A333431 _Robert G. Wilson v_, Mar 20 2020
%E A333431 a(10) from _Giovanni Resta_, Mar 21 2020
%E A333431 a(11)-a(12) from _Vaclav Kotesovec_, Mar 21 2020
%E A333431 a(13)-a(14) from _Vaclav Kotesovec_, Mar 22 2020