On a Waring-Goldbach problem for mixed powers

Abstract

Let $P_r$ denote an almost-prime with at most $r$ prime factors, counted according to multiplicity. In this paper, it is proved, among other results, that, for every sufficiently large, even integer $N$ satisfying the congruence condition $N \not \equiv 2\pmod 3$, the equation \[ N=x^2+p^2+p_1^3+p_2^4+p_3^4+p_4^4 \] is solvable with $x$ being a $P_{5}$ and the other variable primes. This result constitutes an enhancement upon that of Vaughan \cite {s12} and Mu \cite {s9}.