TODOROVA, T. L. Lagrange’s four square theorem with almost-prime numbers having a special form. Mathematics and Education in Mathematics, [S. l.], v. 50, p. 163–175, 2021. Disponível em: https://smb.math.bas.bg/mem/index.php/memjournal/article/view/19. Acesso em: 5 oct. 2026.