  In this paper, it is proved that every sufficiently large even integer can be
represented as the sum of two squares of primes, two cubes of primes, two
biquadrates of primes and 16 powers of 2. Furthermore, there are at least
5.313% odd integers that can be represented as one square of prime, one cube of
prime and one biquadrate of prime. This result constitutes a refinement upon
that of R. Zhang [8].
