One of these scholars was Jabir ibn Aflah, who worked in Islamic Spain in the twelfth century. His methods for solving triangles on the surface of a sphere were translated into both Latin and Hebrew. De revolutionibus was also apparently inspired by Jabir. Islamic mathematicians were also active in trying to deduce Euclid's postulate on parallel lines from the other four postulates of Euclidean geometry. The Greeks, especially the Pythagoreans, were fascinated by numbers.
Amicable numbers are a pair in which each one is the sum of the proper divisors of the other.
It's known that Thabit was just one in a long line of mathematicians who dabbled in number theory, and scholars have found Arab and Hebrew manuscripts of the twelfth and fourteenth centuries that contain details of these studies. But there's a good possibility that people like Fermat had access to a Latin edition. There's no further mention of these rules until the sixteenth century, when Cardano takes note of them in one of his books. Then, the rules appear in a book by Mersenne on music theory, derived in a manner strikingly similar to that used by Levi ben Gerson. It turns out that there happened to be a manuscript of Levi's work in Paris at that time, brought there by the French ambassador to Constantinople.