Kumchev, Angel V. (2005), On the Waring-Goldbach problem for seventh powers, Proceedings of the American Mathematical Society, 133 (10): 2927—2937, doi:10.1090/S0002-9939-05-07908-6, MR2159771
Kumchev, Angel V. (2005), On the Waring-Goldbach problem for seventh powers, Proceedings of the American Mathematical Society, 133 (10): 2927—2937, doi:10.1090/S0002-9939-05-07908-6, MR2159771