Another mathematician, Carl Friedrich Gauss, echoed Archimedes when in 1796 he wrote in his diary, "ΕΥΡΗΚΑ! num = Δ + Δ + Δ", referring to his discovery that any positive integer could be expressed as the sum of at most three triangular numbers.[11] This result is now known as Gauss' Eureka theorem[12] and is a special case of what later became known as the Fermat polygonal number theorem.