Question

Find the smallest natural number m > 90 for which $n=\underset{m-times}{\underset{}{\mathrm{111.....1}}}$ is not a prime number. Hence find the value of $m-87$.

Answer 1

For $m=92,n=(\mathrm{1111...}$ 92 times) is divisible by $11$
as the sum of odd digits is even digits is the same.
Hence, $m-87=5$