Closest Prime

Problem description. You are given an array $a$ (1 indexed)of size $n$. You have to process following operations on the array 1 $l$ $r$ : update elements of indices from $l$ to $r$ inclusive to difference of element and nearest strictly smaller prime (eg: 5 gets updated to 5-3=2). Also note that since 0,1,2 does not have primes below then even after update they remain the same. 2 $l$ $r$ : Sum