A175507 - OEIS

%I #12 Aug 13 2020 14:02:28

%S 7980,8190,9360,10920,11760,11880,12870,13230,13860,14820,15960,16380,

%T 16740,17640,17940,18216,18270,18360,18720,18810,18900,19040,19080,

%U 19140,19656,19740,20196,20580,20790,20880,21168,21560,21840,22176

%N Numbers such that each digit from 0 to 9 appears at least 7 times in the digits of their divisors.

%H Vincenzo Librandi, <a href="/A175507/b175507.txt">Table of n, a(n) for n = 1..1000</a>

%H Erich Friedman, <a href="https://erich-friedman.github.io/numbers.html">What's Special About This Number?</a> (See entry 7980.)

%e 5460 is not in the sequence because the divisors, 1, 2, 3, 4, 5, 6, 7, 10, 12, 13, 14, 15, 20, 21, 26, 28, 30, 35, 39, 42, 52, 60, 65, 70, 78, 84, 91, 105, 130, 140, 156, 182, 195, 210, 260, 273, 364, 390, 420, 455, 546, 780, 910, 1092, 1365, 1820, 2730, 5460, contain the digit 7 only 6 times (namely once in 7, 70, 78, 273, 780 and 2730), which is not enough.

%t fQ[n_] := Block[{s = Transpose@ Tally[ Sort[ Flatten[ IntegerDigits@# & /@ Divisors@ n]]]}, First@ s == {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} && Min@ Last@ s > 6]; k = 1; lst = {}; While[k < 22319, If[ fQ@k, AppendTo[lst, k]]; k++ ]; lst (* _Robert G. Wilson v_, Jul 31 2010 *)

%Y Cf. A059436.

%K base,nonn,easy

%O 1,1

%A _R. J. Mathar_, Jun 02 2010

%E More terms from _Robert G. Wilson v_, Jul 31 2010