|
| |
|
|
A066048
|
|
Product of smallest and greatest prime factors of n.
|
|
8
| |
|
|
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; 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] (* From Harvey P. Dale, June 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) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Nov 08 2009]
|
|
|
CROSSREFS
| Cf. A000040, A001358, A001248, A000961.
Cf. A130064, A130065.
Sequence in context: A204996 A061369 A088377 * A103164 A178147 A005063
Adjacent sequences: A066045 A066046 A066047 * A066049 A066050 A066051
|
|
|
KEYWORD
| nonn,nice,easy
|
|
|
AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com)
|
|
|
EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 03 2002
|
| |
|
|
