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

1,2

Comments

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

Links

Table of n, a(n) for n=1..36.

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 *)

Crossrefs

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

Sequence in context: A178367 A036132 A084968 * A343737 A344473 A230655

Adjacent sequences: A161142 A161143 A161144 * A161146 A161147 A161148

Keyword

nonn,base

Author

Claudio Meller, Jun 03 2009

Extensions

More terms from Claudio Meller, Jun 06 2009

Status

approved