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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

Reinhard Zumkeller

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.)