I Miss Maths

All this working and air traffic control and I've forgotten my Maths background. It's been nearly two years since I considered a serious maths problem. Just the other day I was trying to explain why the passengers are safe in an aircraft if it is struck by lightening because the electromagnetic field inside a hollow conductor is zero. I then claimed I could prove this but realised that I no longer can. I probably couldn't begin to construct an argument let alone a 3 dimensional integral.
But last night Jonath called and was asking about a Maths problem of his. I couldn't answer them but thinking about them was far too enticing. I realise though that I'd never got very far in the subject and becoming a professional mathematician was no where near in sight. Plus I can't stand research. I called a friend from Uni, Stuart, and he couldn't do it either so it made me feel better, but still I didn't have a clue.
So...

© Wolfram Research, Inc.

...I leave you with this which is a picture of the absolute value of the 2-D Fourier transform of the gcd(i,j)