OFFSET
1,2
COMMENTS
This is the subsequence of terms of A069570 with no digit 1 elsewhere than (possibly) in positions k with no prime divisor < 10, i.e., k = 1, 11, 13, 17, 19, ..., 11*11, 127, 131, 137, 139, 11*13, .... - M. F. Hasler, Sep 27 2016
EXAMPLE
54647 is a member but 14647 and 44647 are not members.
13 is a member of A069570 because both 1 and 3 are nonzero, further, 3 is divisible by n = 1 and 1 divides n = 2. 13 is not a member of this sequence because it has a single-digit multiple 3 > 1.
Numbers with "1" in place n = 1 may be in the sequence since 1 divides itself, and 1 does not exceed 1.
21 is a member of this sequence because the digits are nonzero, 1 divides n = 1 and 2 divides n = 2.
MATHEMATICA
Select[Range@ 400, Times @@ Map[Boole, MapIndexed[If[Or[#1 == 0, And[First@ #2 > 1, #1 == 1]], False, Total@ Boole@ {First@ Divisible[#2, #1], First@ Divisible[#1, #2]} > 0] &, Reverse@ IntegerDigits@ #]] > 0 &] (* Michael De Vlieger, Sep 28 2016 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Amarnath Murthy, Mar 24 2002
EXTENSIONS
Definition clarified by M. F. Hasler, Sep 27 2016
Edited by N. J. A. Sloane, Oct 02 2016
STATUS
approved