STEPANETS, O. I.; SHYDLICH, A. L. On one extremal problem for positive series. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 57, n. 12, p. 1677–1683, 2005. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3718. Acesso em: 5 dec. 2025.