Elchin Hasanalizade

Let $\sigma^*(n)$ be the sum of all unitary (i.e. coprime) divisors of $n$. As an analogue of Lehmer’s totient problem, Subbarao proposed the following conjecture. The congruence $\sigma^*(n)\equiv 1\pmod{n}$ is possible iff $n$ is a prime power...

The Fibonacci sequence \(F(n) : (n\geq 0) is the binary recurrence sequence defined by $$ F(0) = F(1) = 1 \qquad \mbox{and} \\ F(n+2) = F(n+1) + F(n) \qquad \forall n \geq 0. $$ There is a broad literature on the Diophantine equations involving the...