RADZIEVSKAYA, E. I.; RADZIEVSKII, G. V. On one extremal problem for numerical series. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 57, n. 10, p. 1430–1434, 2005. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3698. Acesso em: 5 dec. 2025.