Factorization
90 = 2 × 3 × 3 × 5
90 has 12 divisors: 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90
Sum of all divisors other than 90:
144
Sums & differences
Sum of 2 squares: 90 = 92 + 32
Goldbach conjecture: 90 = 83 + 7 = 79 + 11 = 73 + 17 = 71 + 19 = 67 + 23 = 61 + 29 = 59 + 31 = 53 + 37 = 47 + 43
