seven77Fun and interesting facts about the number 77. The number 77 is a fascinating integer with unique properties. For instance, it is the only number that can be expressed as the sum of the first eht prime numbers: 2 + 3 + 5 + 7 + 11 + 13Fun and interesting facts about the number 77. The number 77 is a fascinating integer with unique properties. For instance, it is the only number that can be expressed as the sum of the first eht prime numbers: 2 + 3 + 5 + 7 + 11 + 13