Question 71
The integers from $1$ to $49$ are written in a $7 \times 7$ table, such that for any $k \in \{1, 2, ..., 7\}$, the product of the numbers in the $k$-th row equals the product of the numbers in the $(8-k)$-th row.
a) Prove that there exists a row such that the sum of the numbers written on it is a prime number.
a) Prove that there exists a row such that the sum of the numbers written on it is a prime number.