A284295 - OEIS

%I #7 Sep 08 2022 08:46:19

%S 1,9,11,19,33,91,99,111,119,133,191,199,313,331,339,393,911,919,933,

%T 991,999,1111,1119,1133,1191,1199,1313,1331,1339,1393,1911,1919,1933,

%U 1991,1999,3113,3131,3139,3193,3311,3319,3333,3391,3399,3913,3931,3939,3993

%N Numbers n such that product of digits of n is a power of 9.

%C Supersequence of A284294.

%e 1111 is in the sequence because 1*1*1*1 = 1 = 9^0.

%t FromDigits /@ Select[Join @@ Map[Tuples[{1, 3, 9}, #] &, Range@ 4], IntegerQ@ Log[9, Times @@ #] &] (* _Michael De Vlieger_, Mar 25 2017 *)

%o (Magma) Set(Sort([n: n in [1..10000], k in [0..20] | &*Intseq(n) eq 9^k]))

%Y Cf. Numbers n such that product of digits of n is a power of k for k = 0 - 9: A284375 (k = 0), A002275 (k = 1), A028846 (k = 2), A174813 (k = 3), A284323 (k = 4), A276037 (k = 5), A276038 (k = 6), A276039 (k = 7), A284324 (k = 8), this sequence (k = 9).

%K nonn,base

%O 1,2

%A _Jaroslav Krizek_, Mar 25 2017