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Search: id:A066048
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| A066048 |
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Product of smallest and greatest prime factors of n. |
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+0
8
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| 1, 4, 9, 4, 25, 6, 49, 4, 9, 10, 121, 6, 169, 14, 15, 4, 289, 6, 361, 10, 21, 22, 529, 6, 25, 26, 9, 14, 841, 10, 961, 4, 33, 34, 35, 6, 1369, 38, 39, 10, 1681, 14, 1849, 22, 15, 46, 2209, 6, 49, 10, 51, 26, 2809, 6, 55, 14, 57, 58, 3481, 10, 3721, 62, 21, 4, 65, 22, 4489, 34
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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For all n > 1 a(n) is semiprime; n is semiprime iff a(n) = n; n is prime iff a(n) = n^2;
For all primes p and k > 0, a(p^k) = p^2.
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LINKS
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R. Zumkeller, Table of n, a(n) for n = 1..10000
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FORMULA
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a(n) = A020639(n) * A006530(n).
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MATHEMATICA
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f[n_] := Transpose[ FactorInteger[n]][[1]]; Table[ First[f[n]]*Last[f[n]], {n, 2, 100} ]
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CROSSREFS
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Cf. A000040, A001358, A001248, A000961.
Cf. A130064, A130065.
Sequence in context: A131016 A061369 A088377 this_sequence A103164 A005063 A078615
Adjacent sequences: A066045 A066046 A066047 this_sequence A066049 A066050 A066051
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KEYWORD
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nonn,nice,easy
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com)
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 03 2002
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