OFFSET
1,3
COMMENTS
a(n)^2 divides J_2(n), where J_2 is A007434.
If p > 2 is a prime, a(n) = 2. - Enrique Pérez Herrero, Jan 02 2012
LINKS
Enrique Pérez Herrero, Table of n, a(n) for n = 1..10000
FORMULA
a(n) >= (n*2^(omega(n)-1))/rad(n).
For k>=1, a(2^k) = 2^(k-1) and a(p^k) = 2*p^(k-1) if p is an odd prime. - Amiram Eldar, Feb 20 2023
a(3^n) = A025192(n). - Enrique Pérez Herrero, Jun 05 2023
EXAMPLE
a(56) = gcd(phi(56), psi(56)) = gcd(24, 96) = 24.
MATHEMATICA
JordanTotient[n_, k_:1] := DivisorSum[n, #^k * MoebiusMu[n/#] &] /; (n > 0) && IntegerQ[n]; DedekindPsi[n_] := JordanTotient[n, 2]/EulerPhi[n]; A175732[n_] := GCD[EulerPhi[n], DedekindPsi[n]]; Array[A175732, 100]
f1[p_, e_] := (p - 1)*p^(e - 1); f2[p_, e_] := (p + 1)*p^(e - 1); a[1] = 1; a[n_] := Module[{f = FactorInteger[n]}, GCD[Times @@ f1 @@@ f, Times @@ f2 @@@ f]]; Array[a, 40] (* Amiram Eldar, Feb 20 2023 *)
PROG
(PARI) a(n) = {my(f = factor(n)); gcd(prod(i = 1, #f~, (f[i, 1]-1)*f[i, 1]^(f[i, 2]-1)), prod(i = 1, #f~, (f[i, 1]+1)*f[i, 1]^(f[i, 2]-1))); } \\ Amiram Eldar, Feb 20 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Enrique Pérez Herrero, Aug 24 2010
STATUS
approved