antimorphic number

A number which can be represented both in the form x_0^2 - D y_0^2 and in the form D x_1^2 - y_1^2. This is only possible when the Pell equation x^2 - D y^2 = - 1 is solvable. Then x^2 - D y^2 | = | -(x_0 - D y_0^2)(x_n^2 - D y_n^2) | = | D(x_0 y_n - y_0 x_n)^2 - (x_0 x_n - D y_0 y_n)^2.

idoneal number | polymorph