A174813 a(n) = number whose product of digits equals a power of 3.

1, 3, 9, 11, 13, 19, 31, 33, 39, 91, 93, 99, 111, 113, 119, 131, 133, 139, 191, 193, 199, 311, 313, 319, 331, 333, 339, 391, 393, 399, 911, 913, 919, 931, 933, 939, 991, 993, 999, 1111, 1113, 1119, 1131, 1133, 1139, 1191, 1193, 1199, 1311, 1313, 1319, 1331

Offset

1,2

Comments

Equivalently, numbers whose decimal representation consists of digits from the set {1,3,9}.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Example

a(9)=39 is in the sequence because 3*9=3^3.

Mathematica

Select[Range[2000], IntegerQ[Log[3, Times @@ (IntegerDigits[#])]] &]

Prog

(Haskell)
a174813 n = a174813_list !! (n-1)
a174813_list = f [1] where
   f ds = foldr (\d v -> 10 * v + d) 0 ds : f (s ds)
   s [] = [1]; s (9:ds) = 1 : s ds; s (d:ds) = 3*d : ds
-- Reinhard Zumkeller, Jan 13 2014

Crossrefs

Cf. A028846, A061427.

Sequence in context: A376509 A235583 A287333 * A116444 A215820 A065136

Adjacent sequences: A174810 A174811 A174812 * A174814 A174815 A174816

Keyword

nonn,base

Author

Michel Lagneau, Dec 01 2010

Status

approved