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 A066048 Product of smallest and greatest prime factors of n. 17
 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; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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. LINKS R. Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A020639(n) * A006530(n). MATHEMATICA 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 *) PROG (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 CROSSREFS Cf. A000040, A001358, A001248, A000961. Cf. A130064, A130065. Sequence in context: A061369 A291645 A088377 * A103164 A210966 A300516 Adjacent sequences:  A066045 A066046 A066047 * A066049 A066050 A066051 KEYWORD nonn,nice,easy AUTHOR EXTENSIONS More terms from Robert G. Wilson v, Jan 03 2002 STATUS approved

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Last modified May 19 08:25 EDT 2019. Contains 323389 sequences. (Running on oeis4.)