The $p$-ary function $f(x)$ mapping $\mathrm{GF}(p^{4k})$ to $\mathrm{GF}(p)$given by $f(x)={\rm Tr}_{4k}\big(x^{p^{3k}+p^{2k}-p^k+1}+x^2\big)$ is proven tobe a weakly regular bent function and the exact values of its Walsh transformcoefficients are found. The proof is based on a few new results in the area ofexponential sums and polynomials over finite fields that may also beinteresting as independent problems.
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