77 = 7 x 11.
77 is the number of integer partitions of 12.
77 is the 22nd discrete biprime and the first of the (7.q) family. Since both 7 and 11 are Gaussian primes, this means that 77 is a Blum integer.
77 is the sum of three squares: 77 = 42 + 52 + 62.
77 is the sum of the first eight prime numbers: 77 = 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19.
During World War II in Sweden at the border with Norway, 77 was used as a password, because the tricky pronunciation in Swedish made it easy to instantly discern whether the speaker was native Swedish, Norwegian, or German.
Source: Wikipedia
