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A161145
Numbers which can be expressed as the product of numbers made of only sevens.
7
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
1,2
COMMENTS
49 = 7 * 7; 539 = 7 * 77; 5439 = 7 * 777.
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 *)
KEYWORD
nonn,base
AUTHOR
Claudio Meller, Jun 03 2009
EXTENSIONS
More terms from Claudio Meller, Jun 06 2009
STATUS
approved