1. It is a triangular number.
2. It is the 2nd perfect number. A number is said to be perfect if it is equal to the sum of its perfect divisors except itself.
28 has the factors 1, 2, 4, 7 and 14 that adds up to 28.
All known perfect numbers are even numbers as they end with 6 or 8.
The first five perfect numbers are- 6, 28, 496, 8128 and 33550336.
3. There are 28 days in the month of February except in a leap year when it has 29 days.
4. There are 28 dominoes in a standard double six set.
5. It is a hexagonal number. A hexagonal number is a figurative number.
The formula for the nth hexagonal number is given by --
6. It is the sum of first five consecutive primes.
28 = 2 + 3 + 5 + 7 + 11
7. A 28 side polygon is called Icosikaioctagon.
8. The Gregorian calendar repeats in 28 years. The calendar of 2013 will work in 2041.
9. It can be portioned into 3718 ways.
10. It is the third positive integer with a prime factorization in the form of 22q, where q is an odd prime.
28 = 2 x 2 x 7 = 22 x 7
11. It is used as an approximation to the number of days in the lunar month.
12. The atomic mass of Silicon is 28.
13. The atomic number of Nickel is 28.
14. The revolution time of the surface of the sun on itself is 28 days.
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Dr Rajesh Kumar Thakur
rkthakur1974@gmail.com
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