L = [1, 2, 4, 8, 16, 32, 64]
X = 5

found = False
i = 0
while not found and i < len(L):
   if 2 ** X == L[i]:
       found = True
   else:
       i = i+1

if found:
    print('at index', i)
else:
    print(X, 'not found')