A161147 Numbers which can be expressed as the product of numbers made of only nines.

1, 9, 81, 99, 729, 891, 999, 6561, 8019, 8991, 9801, 9999, 59049, 72171, 80919, 88209, 89991, 98901, 99999, 531441, 649539, 728271, 793881, 809919, 890109, 899991, 970299, 989901, 998001, 999999, 4782969, 5845851, 6554439, 7144929, 7289271, 8010981, 8099919

Offset: 1

Author

Claudio Meller, Jun 03 2009

Keywords

• nonn
• base

Comments

81 = 9 * 9; 891 = 9 * 99; 8991 = 9 * 999.

Crossrefs

Cf. A084034, A161140, A161141, A161142, A161143, A161144, A161145, A161146.

Programs

Mathematica

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 *)
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]

Extensions

More terms from Claudio Meller, Jun 06 2009

Corrected and extended by Harvey P. Dale, Jan 19 2011