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

1,2

Comments

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

Links

Table of n, a(n) for n=1..37.

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]

Crossrefs

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

Sequence in context: A203656 A043087 A037414 * A209220 A207689 A209225

Adjacent sequences: A161144 A161145 A161146 * A161148 A161149 A161150

Keyword

nonn,base

Author

Claudio Meller, Jun 03 2009

Extensions

More terms from Claudio Meller, Jun 06 2009

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

Status

approved