convenient number | Euler's idoneal number | idoneal | suitable number

An idoneal number, also called a suitable number or convenient number, is a positive integer D for which the fact that a number is a monomorph (i.e., is expressible in only one way as x^2 ± D y^2 where x^2 is relatively prime to D y^2) guarantees it to be a prime, prime power, or twice one of these. The numbers are also called Euler's idoneal numbers or suitable numbers. A positive integer n is idoneal iff it cannot be written as a b + b c + c a for integer a, b, and c with 0