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A032917
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Numbers having only digits 1 and 3 in their decimal representation.
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14
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1, 3, 11, 13, 31, 33, 111, 113, 131, 133, 311, 313, 331, 333, 1111, 1113, 1131, 1133, 1311, 1313, 1331, 1333, 3111, 3113, 3131, 3133, 3311, 3313, 3331, 3333, 11111, 11113, 11131, 11133, 11311, 11313, 11331, 11333, 13111, 13113
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OFFSET
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1,2
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COMMENTS
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Numbers n such that product of digits of n is a power of 3. - Vincenzo Librandi Aug 19 2016
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LINKS
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MATHEMATICA
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Flatten[Table[FromDigits[#, 10]&/@Tuples[{1, 3}, n], {n, 5}]] (* Vincenzo Librandi, Jun 02 2012 *)
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PROG
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(Magma) [n: n in [1..14000] | Set(IntegerToSequence(n, 10)) subset {1, 3}]; // Vincenzo Librandi, Jun 02 2012
(PARI) for(n=1, 5, p=2*vector(n, i, 10^(n-i))~; forvec(d=vector(n, i, [1, 3]/2), print1(d*p, ", "))) \\ M. F. Hasler, Mar 10 2014
(Python)
def a(n): return int(bin(n+1)[3:].replace('1', '3').replace('0', '1'))
(Python)
def A032917(n): return (int(bin(m:=n+1)[3:])<<1) + (10**(m.bit_length()-1)-1)//9 # Chai Wah Wu, Oct 13 2023
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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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EXTENSIONS
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STATUS
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approved
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