Everyone has heard of the fact that 1729 is interesting because it is the smallest positive integer expressible as the sum of two cubes in two ways:

1729 = 9^3 + 10^3
1729 = 1^3 + 12^3

Can anyone think of the corresponding number for biquadrates? It is certainly very large. If not, can anyone give a tidy estimate of its order of magnitude?

But if anyone could tell me something interesting about the number 51 I would be HUGELY grateful. It's part of a bet I made with someone where I said that every number had something interesting about it after we started talking about the number 26 being the only number that lies between a square and a cube.

I did have something on 51, but didn't write it down and now can't remember what it was and can't work it out 🙁 Anyone?

After wasting the last ten minutes of my life using google I have found what I was looking for:-

"51

51 is the the first "boring" number according to David Wells' book "Curious and Interesting Numbers", i.e. it is the first positive integer not to appear.

Actually, an interesting thing about 51 is that it is the first odd composite number not to appear in times tables (which traditionally went up to 12 times), which means that it is probably the first number that many people would fail to recognise as being composite."

Taken from http://www.1729.com/topics/51.html

Come to think of it though, the very fact that it's the first "boring" positive integer to appear in that book makes it highly fascinating!