The Prime Number would be 41 because prime numbers are numbers that cannot be multiplied into it excluding itself and 1.
16 can be multiplied into with 4 x 4 or 8x2
24 can be multiplied into with 6x4 or 8x3 or 12x2
41 cannot be multiplied other than 41x1
64 can be multiplied into with 8x8, 4x16, 2x32