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 A045509 #18 Jul 19 2020 02:12:56 %S A045509 1,120,1307674368000,121645100408832000,1124000727777607680000, %T A045509 15511210043330985984000000,10888869450418352160768000000, %U A045509 10333147966386144929666651337523200000000,13763753091226345046315979581580902400000000 %N A045509 Factorials having initial digit '1'. %C A045509 Benford's law shows that this sequence will contain about log 2/log 10 =~ 30% of factorials. [_Charles R Greathouse IV_, Nov 13 2010] %H A045509 <a href="/index/Be#Benford">Index entries for sequences related to Benford's law</a> %F A045509 a(n) = A000142(A045520(n+1)). - _Amiram Eldar_, Jul 19 2020 %t A045509 Select[Range[40]!,First[IntegerDigits[#]]==1&] (* _Harvey P. Dale_, Aug 06 2013 *) %Y A045509 For factorials with initial digit d (1 <= d <= 9) see A045509, A045510, A045511, A045516, A045517, A045518, A282021, A045519; A045520, A045521, A045522, A045523, A045524, A045525, A045526, A045527, A045528, A045529. %Y A045509 Cf. A000142. %K A045509 nonn,base %O A045509 1,2 %A A045509 _Jeff Burch_ %E A045509 Corrected and extended by _Harvey P. Dale_, Aug 06 2013