Consider the minterm list form of a Boolean function 𝐹 given below. 𝐹(𝑃,𝑄,…

Consider the minterm list form of a Boolean function 𝐹 given below.

𝐹(𝑃,𝑄, 𝑅, 𝑆) = ∑𝑚(0, 2, 5, 7, 9, 11) + 𝑑(3, 8, 10, 12, 14)

Here, 𝑚 denotes a minterm and 𝑑 denotes a don’t care term. The number of essential prime implicants of the function 𝐹 is ______.