The number of solutions of .
The distribution of totients.
Divisors of the Euler and Carmichael functions
Sign changes in
The jumping champions of the Farey series
On square values of the product of the Euler totient and sum of divisors functions
If n is a positive integer such that ϕ(n)σ(n) = m² for some positive integer m, then m ≤ n. We put m = n-a and we study the positive integers a arising in this way.
On non-intersecting arithmetic progressions
We improve known bounds for the maximum number of pairwise disjoint arithmetic progressions using distinct moduli less than x. We close the gap between upper and lower bounds even further under the assumption of a conjecture from combinatorics about Δ-systems (also known as sunflowers).
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