A161145 Numbers which can be expressed as the product of numbers made of only sevens.

1, 7, 49, 77, 343, 539, 777, 2401, 3773, 5439, 5929, 7777, 16807, 26411, 38073, 41503, 54439, 59829, 77777, 117649, 184877, 266511, 290521, 381073, 418803, 456533, 544439, 598829, 603729, 777777, 823543, 1294139, 1865577, 2033647, 2667511, 2931621

Offset: 1

Author

Claudio Meller, Jun 03 2009

Keywords

• nonn
• base

Comments

49 = 7 * 7; 539 = 7 * 77; 5439 = 7 * 777.

Crossrefs

Cf. A084034, A161140, A161141, A161142, A161143, A161144, A161146, A161147.

Programs

Mathematica

Module[{upto=3*10^6,sevs=Table[FromDigits[PadRight[{},n,7]],{n,7}]},Select[ Union[ Flatten[Table[Times@@@Tuples[sevs,i],{i,7}]]],#<=upto&]] (* Harvey P. Dale, Feb 10 2015 *)

Extensions

More terms from Claudio Meller, Jun 06 2009