A285803 - OEIS

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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

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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.