I’ve long found the fascination with celebrating milestones that have no intrinsic worth to be somewhat puzzling, why should we make more effort for birthdays falling on a multiple of ten than those that come just before or after? There is nothing about the number itself that makes such a milestone special.

In this vein I decided that rather than trumpet my 200th post I would pick a number that is more interesting (and closer). So, welcome to my 191st blog entry. Compared to some of my more prolific colleagues on Sciblogs and in the blogosphere 191 posts over a period of almost 3yrs is practically laughable but you work with what you’ve got.

So, why 191? Well according to the Oracle of Wikipedia this number has many special features.

191 is an odious number, apparently numbers can be categorised as either odious or evil. This is a reference to it’s properties when converted into binary. As you are likely aware the binary system represents numbers as strings of zeroes and ones. For example the number six can be represented as 110, the number 191 is represented by the string 10111111. A number is evil if there are an even number of 1s in the string (like number 6) and odious if the number of 1s is odd. Those mathematicians are a funny bunch. (play with binary here)

The number is a prime, and apparently there are a large number of prime flavours and this one has quite a few. It is a palindromic prime number, and not only that it is the smallest such prime that you also get a palindromic prime number when you sum the individual numbers.

191 is a Chen prime, which mean if you add 2 to it you also get a prime (or the product of two primes, but in this case a prime).

It is also the first number of a prime quadruplet, so that in addition to adding 2 and getting a prime as above you can also add 6 and 8 and still get primes as well.

Sophie Germain prime numbers occur when you can multiply a prime number by 2, add 1 and get another prime. Guess what, 191 is one of these too.

Those were the less esoteric prime properties that 191 displays. Aren’t you glad I didn’t keep going?

191 is also a Thabit number, or a number that can be arrived at using the formula 3 x 2^{n} – 1. ie run this formula and plug values into the exponent position *n* and you will get a series of numbers of which 191 is one (*n*=6 BTW). This formula can be used to generate a sort of number called Amicable numbers, but beyond that I have no idea why this would matter.

Finally 191 is the atomic number of a theoretical element called Unununium, sounds like the start of a sneeze.

There you go, 191 is way more interesting than a boring number like 200. A far better choice for celebration.

Still on the topic of numbers here’s a visually stunning video looking at numbers in nature, specifically the Fibonacci sequence.