78

78 = 2 x 3 x 13.

78 has a unique representation as a sum of three squares: 78 = 2² + 5² + 7².

78 is the smallest number with seven representations as a sum of two primes: 78 = 5 + 73 = 7 + 71, 11 + 67 = 17 + 61 = 19 + 59 = 31 + 47 = 37 + 41.

78 is the twelfth triangular number. According to the song "The Twelve Days of Christmas," 78 gifts were sent on the twelfth day.

78 is 66 in base 12.

A 78 is an old type of gramophone record playing at 78 revolutions per minute.

Source: Phillips, R. 2004. Numbers: Facts, Figures and Fiction. Badsey Publications.