45 (forty-five) is the natural number following 44 and followed by 46. In mathematics Forty-five is a triangular number, a hexagonal and 16-gonal number, a Kaprekar number, and a Harshad number. 45 is the sixth positive integer with a prime factorization of the form p2q, with p and q being prime. 33 is the aliquot sum of 45 and the aliquot sequence of 45 is (45,33,15,9,4,3,1,0). Since the greatest prime factor of 452 + 1 = 2026 is 1013, which is clearly more than 45 twice, 45 is a Størme… (More on Xlv)