## Sunday, June 28, 2015

### Special properties of number 28 (Today’s Date)

1. 28 is a triangular number since it is the sum of the first seven counting numbers: 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28.
2. 28 is also a perfect number since the sum of its aliquot divisors (factors that are less than the number itself) is also 28. The aliquot factors of 28 are 1, 2, 4, 7, and 14, and 1 + 2 + 4 + 7 + 14 = 28. The next smallest perfect number is 6, and the next highest perfect number is 496.
3. 28 is an example of a happy number. When you square the digits, add them, and repeat this process on the resulting number, you eventually end up with 1:
2^2 + 8^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1
4. The sum of the first five prime numbers is 2 + 3 + 5 + 7 + 11 = 28.
5. 28 is a hexagonal number, but not a centered hexagonal number. Every hexagonal number is also a triangular number, but not every triangular number is a hexagonal number.
6. A polygon with 28 sides is called an icosikaioctagon.
7. Between the years 2000 and 2099, the calendar repeats every 28 years. It also cycles every 28 years between 2101 and 2199.