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A066048
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Product of smallest and greatest prime factors of n.
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18
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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
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OFFSET
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1,2
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COMMENTS
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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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FORMULA
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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} ]
p[n_]:=Module[{fctrs=Transpose[FactorInteger[n]][[1]]}, First[fctrs] Last[fctrs]]; Array[p, 70] (* Harvey P. Dale, Jun 11 2011 *)
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PROG
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(PARI) { for (n = 1, 10000, if (n==1, a=1, f=factor(n)~; a=f[1, 1] * f[1, length(f)]); write("b066048.txt", n, " ", a) ) } \\ Harry J. Smith, Nov 08 2009
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CROSSREFS
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KEYWORD
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nonn,nice,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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