780 is a triangular number, the sum of the positive integers from 1 to 39.
780 = (5 + 7) × (5 + 8) × (5 + 0).
780 is the sum of ten consecutive primes: 59 + 61 + 67 + 71 + 73 + 79 + 83 + 89 + 97 + 101 = 780.
Telephone area code 780 covers Edmonton, Alberta.
Source: What’s Special About This Number
