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 A161147 #19 May 19 2019 12:44:15
%S A161147 1,9,81,99,729,891,999,6561,8019,8991,9801,9999,59049,72171,80919,
%T A161147 88209,89991,98901,99999,531441,649539,728271,793881,809919,890109,
%U A161147 899991,970299,989901,998001,999999,4782969,5845851,6554439,7144929,7289271,8010981,8099919
%N A161147 Numbers which can be expressed as the product of numbers made of only nines.
%C A161147 81 = 9 * 9; 891 = 9 * 99; 8991 = 9 * 999.
%t A161147 ns=Table[10^i-1,{i,7}]; Take[Union[Join[ns, Flatten[Table[Times@@@Tuples[ns,x], {x,2,8}]]]],50] (* _Harvey P. Dale_, Jan 19 2011 *)
%t A161147 nMax=10^7; ns=Table[10^i-1, {i,Floor[Log[10,nMax]]}]; u={1}; Do[While[u2=Union[u, Select[i*u, # <= nMax&]]; u != u2, u=u2], {i,ns}]; Rest[u]
%Y A161147 Cf. A084034, A161140, A161141, A161142, A161143, A161144, A161145, A161146.
%K A161147 nonn,base
%O A161147 1,2
%A A161147 _Claudio Meller_, Jun 03 2009
%E A161147 More terms from _Claudio Meller_, Jun 06 2009
%E A161147 Corrected and extended by _Harvey P. Dale_, Jan 19 2011