Find the minimum number of subarrays needed to validly split each prefix of the input array a.

Denote dp[i] as the minimum number of subarrays needed to validly split [a[0], a[1], … , a[i - 1]], where dp[0] = 0.

Think about the dynamic programming transitions.

If we split the first i elements of the array, the last subarray in this splitting will end with a[i - 1] and start with some a[j], where gcd(a[j], a[i - 1]) ≠ 1. Then, we need to validly split the first j elements of the array, or [a[0]…a[j - 1]].

Iterate over all possible j < i such that gcd(a[j], a[i - 1]) ≠ 1 and let dp[i] = min(dp[i], dp[j] + 1).