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