OFFSET
1,4
COMMENTS
a(n) = exp(-Sum_{d in P} moebius(d)*log(n/d)) where P = {d : d divides n and d is prime}. This is a variant of the (exponential of the) von Mangoldt function where the divisors are restricted to prime divisors. The (exponential of the) summatory function is A205957. Apart from n=1 the value is 1 if and only if n is prime; the fixed points are the products of two distinct primes (A006881).
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Peter Luschny, The von Mangoldt Transformation.
FORMULA
a(n) = Product_{p|n} n/p. - Charles R Greathouse IV, Jun 27 2013
If n is squarefree, then a(n) = n^(omega(n)-1). - Wesley Ivan Hurt, Jun 09 2020
a(p^e) = p^(e-1) for p prime, e > 0. - Bernard Schott, Jun 09 2020
MAPLE
with(numtheory): A205959 := proc(n) select(isprime, divisors(n));
simplify(exp(-add(mobius(d)*log(n/d), d=%))) end:
# Alternative:
a := n -> local p; mul(n/p[1], p in ifactors(n)[2]):
seq(a(n), n = 1..68); # Peter Luschny, Jul 19 2023
MATHEMATICA
a[n_] := Exp[-Sum[ MoebiusMu[d]*Log[n/d], {d, FactorInteger[n][[All, 1]]}]]; Table[a[n], {n, 1, 68}] (* Jean-François Alcover, Jan 15 2013 *)
PROG
(Sage)
def A205959(n) :
P = filter(is_prime, divisors(n))
return simplify(exp(-add(moebius(d)*log(n/d) for d in P)))
[A205959(n) for n in (1..60)]
(PARI) a(n)=my(f=factor(n)[, 1]); prod(i=1, #f, n/f[i]) \\ Charles R Greathouse IV, Jun 27 2013
(Haskell)
a205959 n = product $ map (div n) $ a027748_row n
-- Reinhard Zumkeller, Dec 15 2013
(Python)
from math import prod
from sympy import primefactors
def A205959(n): return prod(n//p for p in primefactors(n)) # Chai Wah Wu, Jul 12 2023
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
Peter Luschny, Feb 03 2012
EXTENSIONS
New name from Charles R Greathouse IV, Jun 30 2013
STATUS
approved