129 is a fabulous number. It is one of my favourites.
For a start, it is the sum of the first ten prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29. I know this because the sum of the first nine is 100 – a fact that not many people know I would imagine.
1, by the way, is not a prime number. In fact, most early Greeks did not even consider 1 to be a number, and so they certainly did not consider it a prime. Times moved on, of course, and in the 19th century, many mathematicians did consider the number 1 a prime. For example, the number 15 can be factored as 3 x 5 or 1 x 3 x 5. If 1 were prime, these would be considered different factorizations of 15 into prime numbers.
Anyway, that’s the first reason. The second is that it is the smallest number that can be expressed as a sum of three squares in four different ways:
- 11² + 2² + 2²
- 10² + 5² + 2²
- 8² + 8² + 1²
- 8² + 7² + 4²
Thirdly, 129 is a happy number, so how can it not be liked?! A happy number begins with any positive integer (a whole number), which is then replaced by the sum of the squares of its digits, which gets repeated until the number equals 1. If this process creates an endless loop which never reaches 1 – such a number is unhappy.
For 129, this is the process:
- 129 –> 1² + 2² + 9² = 86
- 86 –> 8² + 6² = 100
- 100 –> 1² + 0² + 0² = 1
There you go. Tells you nothing about my day. But I’ve done nothing as exciting as the number 129 today.
