28

[xy_jarik]

Twenty-eight is a harmonic divisor number, a happy number, a triangular number, a hexagonal number,and a centered nonagonal number. Twenty-eight is the sum of the first five prime numbers, and the sum of the totient function for the first nine integers.

Twenty-eight is the ninth and last number in early Indian magic square of order 3.

There are

Comments

[the_svin]

28 in HeXodecimal is 1C (так и хочется дописать "бухгалтерия").