A285803 Numbers k such that both k and 2k contain the digit 7.

37, 87, 137, 187, 237, 287, 337, 357, 367, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 387, 397, 437, 487, 537, 587, 637, 687, 735, 736, 737, 738, 739, 785, 786, 787, 788, 789, 837, 857, 867, 870, 871, 872, 873, 874, 875, 876, 877, 878, 879, 887, 897, 937

Offset

1,1

Links

Table of n, a(n) for n=1..53.

Example

37 is in the sequence because 2 * 37 = 74, which has one 7.
47 is not in the sequence because 2 * 47 = 94, which has no 7's.

Mathematica

Select[Range[10^3], Times @@ Boole@ Map[DigitCount[#, 10, 7] > 0 &, # {1, 2}] > 0 &] (* Michael De Vlieger, Apr 26 2017 *)

Crossrefs

Cf. A039938.

Sequence in context: A044556 A350003 A330362 * A157043 A246930 A142525

Adjacent sequences: A285800 A285801 A285802 * A285804 A285805 A285806

Keyword

nonn,base

Author

J. Lowell, Apr 26 2017

Status

approved