OFFSET
1,4
COMMENTS
n is squarefree iff a(n)=1.
Product of primes dividing n more than once. - Charles R Greathouse IV, Aug 08 2013
Squarefree kernel of the square part of n. - Peter Munn, Jun 12 2020
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Squarefree.
FORMULA
Multiplicative with p^e -> p^ceiling((e-1)/e), p prime.
a(n) = rad(n/rad(n)) = A007947(A003557(n)). - Velin Yanev, Antti Karttunen, Aug 20 2017, Nov 28 2017
Dirichlet g.f.: zeta(s) * Product_{p prime} (1 + 1/p^(2*s-1) - 1/p^(2*s)). - Amiram Eldar, Nov 09 2023
MATHEMATICA
Table[With[{r = Apply[Times, FactorInteger[n][[All, 1]]]}, GCD[r, n/r]], {n, 104}] (* Michael De Vlieger, Aug 20 2017 *)
PROG
(PARI) a(n)=my(f=factor(n)); prod(i=1, #f~, f[i, 1]^(f[i, 2]>1)) \\ Charles R Greathouse IV, Aug 08 2013
CROSSREFS
KEYWORD
nonn,easy,mult
AUTHOR
Reinhard Zumkeller, Jun 24 2002
STATUS
approved