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A050677
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Number of prime factors of concatenation of numbers from n down to 1, with multiplicity.
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8
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1, 2, 2, 2, 3, 2, 2, 4, 5, 3, 2, 3, 3, 4, 6, 4, 7, 10, 4, 5, 4, 5, 4, 5, 6, 9, 9, 5, 7, 8, 3, 6, 5, 7, 9, 8, 4, 3, 6, 5, 8, 6, 3, 8, 7, 5, 7, 7, 3, 6, 3, 7, 12, 14, 3, 5, 4, 6, 3, 3, 5, 9, 6, 6
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OFFSET
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1,2
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COMMENTS
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Strictly speaking a(1) = 0.
Smallest number not yet factored is 656463...4321.
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LINKS
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Table of n, a(n) for n=1..64.
P. De Geest, Reversed Smarandache Concatenated Numbers, Prime factors from n down to 1
C. Rivera, Primes by Listing
M. Fleuren, Factors and primes of Smarandache sequences.
M. Fleuren, Smarandache Factors and Reverse factors
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EXAMPLE
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21 = 3*7 so a(2) = 2; 321 = 3*107 so a(3) =2; 4321 = 29*149 so a(4) = 2; etc.
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MATHEMATICA
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Join[{1}, Table[PrimeOmega[FromDigits[Flatten[IntegerDigits[Range[i, 1, -1]]]]], {i, 2, 36}]] (* Jayanta Basu, May 30 2013 *)
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CROSSREFS
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Cf. A000422, A046460, A050679-A050682.
Sequence in context: A099774 A142240 A048288 * A058013 A223934 A031356
Adjacent sequences: A050674 A050675 A050676 * A050678 A050679 A050680
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KEYWORD
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nonn,base,hard
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AUTHOR
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Patrick De Geest, Aug 15 1999.
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STATUS
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approved
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