OFFSET
1,2
COMMENTS
A permutation of A323333. - Amiram Eldar, Sep 19 2020
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
Dirichlet g.f.: zeta(s-1)*Product_{p prime} (1 - 2*p^(1-s) + p^(2-s)), corrected by Vaclav Kotesovec, Dec 18 2019
Multiplicative with a(p^e) = p*(p-1)*p^(e-1).
a(2^e) = 2^e. (Special case of above.) - Omar E. Pol, Feb 19 2018
A003557(n) | a(n). - R. J. Mathar, Feb 26 2018
From Vaclav Kotesovec, Dec 18 2019: (Start)
Dirichlet g.f.: zeta(s-1) * zeta(s-2) * Product_{primes p} (1 + 2*p^(3-2*s) - p^(4-2*s) - 2*p^(1-s)).
Sum_{k=1..n} a(k) ~ c * Pi^2 * n^3 / 18, where c = A065473 = Product_{primes p} (1 - 3/p^2 + 2/p^3) = 0.2867474284344787341078927... (End)
Sum_{n>=1} 1/a(n) = Product_{p prime} (1 + 1/(p-1)^2) = 2.826419... (A065485). - Amiram Eldar, Sep 19 2020
G.f. for a signed version of the sequence: Sum_{n >= 1} mu(n)*n^2*x^n/(1 - x^n)^2 = Sum_{n >= 1} (-1)^omega(n)*a(n)*x^n = x - 2*x^2 - 6*x^3 - 4*x^4 - 20*x^5 + 12*x^6 - 42*x^7 - 8*x^8 - 18*x^9 + 40*x^10 - ..., where mu(n) is the Möbius function A008683(n) and omega(n) = A001221(n) is the number of distinct primes dividing n. - Peter Bala, Mar 05 2022
MAPLE
MATHEMATICA
Array[EulerPhi[#] SelectFirst[Reverse@ Divisors@ #, SquareFreeQ] &, 58] (* Michael De Vlieger, Feb 20 2018 *)
f[p_, e_] := (p-1)*p^e; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Sep 19 2020 *)
PROG
(PARI) a(n) = eulerphi(n)*factorback(factorint(n)[, 1]); \\ Michel Marcus, Jun 24 2019
CROSSREFS
KEYWORD
nonn,mult,easy
AUTHOR
R. J. Mathar, Feb 19 2018
STATUS
approved