OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Jean-Marie De Koninck and Florian Luca, On the composition of the Euler function and the sum of divisors function, Colloquium Mathematicum, Vol. 108, No. 1 (2007), pp. 31-51.
FORMULA
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k)/A289412(k) = (Pi^4/36) * Product_{p prime} (1 + 2/p^3 - 1/p^5) = 3.6174451656... . - Amiram Eldar, Nov 21 2022
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} A289412(k)/a(k) = Product_{p prime} (1 - 3/(p*(p + 1)) + 1/(p^2*(p + 1)) + ((p-1)^3/p^2)*Sum_{k>=3} 1/(p^k-1)) = 0.45782563109026414241... (De Koninck and Luca, 2007). - Amiram Eldar, Feb 27 2024
EXAMPLE
Fractions begin with: 1, 3, 2, 7/2, 3/2, 6, 4/3, 15/4, 13/6, 9/2, 6/5, 7, ...
For n = 7, sigma(7) / phi(7) = 8/6 = 4/3, a(7) = 4.
MATHEMATICA
Array[Numerator[DivisorSigma[1, #]/EulerPhi[#]] &, 71] (* Michael De Vlieger, Aug 19 2017 *)
PROG
(Magma) [Numerator(SumOfDivisors(n) / EulerPhi(n)): n in[1..1000]]
(PARI) a(n) = numerator(sigma(n)/eulerphi(n)); \\ Michel Marcus, Aug 21 2017
CROSSREFS
KEYWORD
nonn,easy,frac
AUTHOR
Jaroslav Krizek, Aug 19 2017
STATUS
approved