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A069571
Numbers n in which the k-th digit (counted from the right) is nonzero and is either a divisor of k (but not 1 in case k has a single-digit prime divisor) or a multiple of k, for all 1 <= k <= number of digits of n.
4
1, 2, 3, 4, 5, 6, 7, 8, 9, 21, 22, 23, 24, 25, 26, 27, 28, 29, 41, 42, 43, 44, 45, 46, 47, 48, 49, 61, 62, 63, 64, 65, 66, 67, 68, 69, 81, 82, 83, 84, 85, 86, 87, 88, 89, 321, 322, 323, 324, 325, 326, 327, 328, 329, 341, 342, 343, 344, 345, 346, 347, 348, 349, 361, 362
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
Cf. A069570.
Sequence in context: A076105 A094280 A082323 * A039173 A103951 A342304
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