Let k be a positive integer with k≥5\documentclass[12pt]{minimal}
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\begin{document}$$k \ge 5$$\end{document}, λ1,λ2,λ3,λ4\documentclass[12pt]{minimal}
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\begin{document}$$\lambda _1, \lambda _2, \lambda _3, \lambda _4$$\end{document} be nonzero real numbers, not all of the same sign, with λ1/λ2\documentclass[12pt]{minimal}
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\begin{document}$$\lambda _1/\lambda _2$$\end{document} irrational and algebraic. Suppose that V\documentclass[12pt]{minimal}
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\begin{document}$${\mathcal {V}}$$\end{document} is a well-spaced sequence and δ>0\documentclass[12pt]{minimal}
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\begin{document}$$\delta >0$$\end{document}. By E4k(V,X,δ)\documentclass[12pt]{minimal}
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\begin{document}$$E_{4k}({\mathcal {V}}, X, \delta )$$\end{document}, we denote the number of v∈V\documentclass[12pt]{minimal}
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\begin{document}$$v \in {\mathcal {V}}$$\end{document} with v≤X\documentclass[12pt]{minimal}
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\begin{document}$$v \le X$$\end{document} for which |λ1p12+λ2p22+λ3p34+λ4p4k-v|<v-δ\documentclass[12pt]{minimal}
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\begin{document}$$\begin{aligned} |\lambda _1 p_1^2 + \lambda _2 p_2^2+ \lambda _3 p_3^4+ \lambda _4 p_4^k - v| < v^{-\delta } \end{aligned}$$\end{document}has no solution in primes p1,p2,p3,p4\documentclass[12pt]{minimal}
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\begin{document}$$p_1,p_2,p_3,p_4$$\end{document}. In this paper, it is proved that E4k(V,X,δ)≪X1-σ(k)+2δ+ε\documentclass[12pt]{minimal}
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\begin{document}$$E_{4k}({\mathcal {V}}, X, \delta ) \ll X^{1-\sigma (k)+2\delta +\varepsilon }$$\end{document}, where σ(k)\documentclass[12pt]{minimal}
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\begin{document}$$\sigma (k)$$\end{document} relies on k. This result constitutes a refinement upon that of Qu and Zeng (Diophantine approximation with prime variables and mixed powers. Ramanujan J 52:625–639, 2020).
