2022 SSMO Speed Round Problems/Problem 6

Problem

At the beginning of day $1$, there is a single bacterium in a petri dish. During each day, each bacterium in the petri dish divides into $a>1$ new bacteria, and $b\ge 1$ bacteria are added to the petri dish (these bacteria do not divide on the day they were added). For example, at the end of day $1$, there are $a+b$ bacteria in the petri dish. If, at the end of day $4$, the number of bacteria in the petri dish is a multiple of $48$, find the minimum possible value of $a+b$.

Solution