Bernard Frénicle de Bessy

Bernard Frénicle de Bessy (c. 1604 – 1674), was a French mathematician born in Paris, who wrote numerous mathematical papers, mainly in number theory and combinatorics.

He is also remembered for his treatise Traité des triangles rectangles en nombres published (posthumously) in 1676[1] and reprinted in 1729.

[2] Bessy was a member of many of the scientific circles of his day, including the French Academy of Sciences, and corresponded with many prominent mathematicians, such as Mersenne and Pascal.

He considers the case where the integer is 221 and promptly applies his second rule, which states that "if you do not know, even generally, what is proposed, find its properties by systematically constructing similar numbers."

Frénicle instead relied on structured and careful observations to find interesting patterns and constructions rather than producing proofs in the axiomatic Euclidean sense.