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A174813
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a(n) = number whose product of digits equals a power of 3.
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10
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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
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OFFSET
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1,2
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COMMENTS
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Equivalently, numbers whose decimal representation consists of digits from the set {1,3,9}.
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LINKS
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EXAMPLE
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a(9)=39 is in the sequence because 3*9=3^3.
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MATHEMATICA
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Select[Range[2000], IntegerQ[Log[3, Times @@ (IntegerDigits[#])]] &]
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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