Most of us have studied, ‘**Numbers’ as Quantity**, an amount that can be counted. But do we use numbers just for counting? Take a pause and think of different places you see numbers (that are not meant for counting)

That’s correct, the list goes on – Your room number, building number, lane number or sector number, Pin Code, Latitude and Longitude…wait a second! in short we are thinking about address or locating a place on Earth. (*Thought Bubble* – How does GPS work?)

GPS reminds me of geography where we see numbers in the weather chart, measurement of physical landforms, depth of oceans and the thickness of ozone (which is depleting)…Oh wait did forget to mention time, date and year with respect to history or the binary code in machine languages. In fact, every domain of knowledge is filled with numbers.

In daily life, we have numbers like Mobile number, Passport number, Adhaar number (if you live in India) or your account number. In short we can say that numbers are used for identification too. They act as a unique key (primary key for computer science graduates). I know some of you may think of more than one bus with the same number like two buses having number 7 and going from point A to B. But let me clarify here, it’s basically the route number. For example, if you visit England the number 9 **bus route** is one of the best ways to see some of the chicest streets in all of **London**.

Earlier we mentioned India and now England, there is so much to talk about the two great countries and their common history. For today, let’s stick to one – **The number 1729**!

Yes, it’s the **Hardy-Ramanujan number**. When you read Srinivasa Ramanujan’s biography ** ‘The Man Who Knew Infinity’** by Robert Knaigel you will come across this interesting anecdote where G. H. Hardy had gone to visit S. Ramanujan in hospital. Mr. Hardy quipped that he came in a taxi with the number ‘1729’ which seemed a fairly ordinary number. Ramanujan said that it was not. It is the smallest number which can be expressed as the sum of two different cubes in two different ways. I hope you got that right, have a look at the two ways:

1729 is the sum of the cubes of 12 and 1. Cube of 12 is 1728 and cube of 1 is 1; adding the two results in 1729.

1729 is also the sum of the cubes of 10 and 9. Cube of 10 is 1000 and cube of 9 is 729; adding the two numbers results in 1729.

Numerically it can be written as 1729 = 1^{3} + 12^{3} = 9^{3} + 10^{3}

Apart from this special feature 1729 is also a *Zeisel number*, third *Carmichael number* and the first absolute *Euler pseudoprime*. No wonder when two extra ordinary mathematicians meet the resultant has to be something special. I wish I could contact the taxi guy (in which G.H. Hardy came to visit S.Ramanujan) and inform him about the great taxi he was riding.

(*Thought Bubble *– What is your vehicle number? Try and make some interesting combination & do share it with us)

PS: Since 2012, 22nd December is celebrated as National Mathematics Day in India to honour S. Ramanujan. Who was born on 22/10/1887.