Multiplying an array by a mpf number just works:
import numpy as np
import mpmath as mp
small_number = mp.besseli(400, 2) # This is an mpf number
# Note that creating a list using `range` and then converting it
# to an array is not very efficient. Do this instead:
A = np.arange(600)
result = small_number * A # Array of dtype object, ie, it contains mpf numbeers
Multiplying element-wise two arrays containing mpf numbers also works:
result * result
So your real problem is how to evaluate an mpmath function in a numpy array. To do that, I'd use np.frompyfunc
(some time ago this was the only option).
besseli_vec = np.frompyfunc(mp.besseli, 2, 1)
besseli_vec(0, A)