1. Equations in quaternions;Niven;The American Mathematical Monthly,1941
2. Sur les équations polynomiales dans les quaternions;Beck;L'Enseignement Mathématique,1979
3. Polynomials with coefficients from a division ring;Bray;Can. J. Math,1983
4. On the zeros of polynomials over division rings;Gordon;Trans. Amer. Math. Soc.,1965
5. R. Spira, The complex and quaternion sum of divisors inequality, (private communication).