A386402 a(n) = denominator(sigma(n)*phi(n)/n^2).

1, 4, 9, 8, 25, 3, 49, 16, 27, 25, 121, 9, 169, 49, 75, 32, 289, 18, 361, 25, 147, 121, 529, 6, 125, 169, 81, 7, 841, 25, 961, 64, 363, 289, 1225, 108, 1369, 361, 507, 10, 1681, 49, 1849, 121, 225, 529, 2209, 36, 343, 125, 289, 169, 2809, 27, 605, 49, 361, 841, 3481, 75

Offset

1,2

Comments

A386401(n)/a(n) = sigma(n)*phi(n)/n^2 is a multiplicative function since it is the product of three multiplicative functions.

References

James J. Tattersall, Elementary Number Theory in Nine Chapters, Cambridge University Press, 1999, Exercise 5.3.21 on page 169.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Mathematica

a[n_]:=Denominator[DivisorSigma[1, n]EulerPhi[n]/n^2]; Array[a, 60]

Prog

(PARI) a(n) = {my(f = factor(n)); denominator(sigma(f) * eulerphi(f) / n^2); } \\ Amiram Eldar, Jul 21 2025

Crossrefs

Cf. A000010, A000203, A000290.

Cf. A386401 (numerators).

Sequence in context: A257851 A133790 A316346 * A135718 A140580 A289280

Adjacent sequences: A386399 A386400 A386401 * A386403 A386404 A386405

Keyword

nonn,easy,frac

Author

Stefano Spezia, Jul 20 2025

Status

approved