Birkhaeuser, Boston, 1984; see p. 188. P. Weinberger, Exponents of the class groups of complex quadratic fields, Acta Arith., 22 (1973), 117–124. Ernst Kani, Idoneal Numbers And Some Generalizations, Ann. Sci. Math. Québec 35, No 2, (2011), 197-227. External links K. S. Brown, Mathpages, Numeri Idonei M. Waldschmidt, Open Diophantine problems Integer sequences Unsolved problems in number theory Leonhard Euler