How To Use Rice And A Chessboard To Find Primes !

I love this little piece of maths and the fact that security on the internet all relies on large prime numbers!

Fantastic Number

Legend has it that Chess was invented in India by a mathematician. The King was so grateful to the mathematician that he asked him to name any prize as a reward. The inventor thought for a minute, then asked for 1 grain of rice to be placed on the first square of the chessboard, 2 on the second, 4 on the third, 8 on the fourth, and so on, so that each square got twice as many grains of rice as were on the previous square.

The King readily agreed, astonished that the mathematician wanted so little – but he was in for a shock. When he began to place rice on the board, the first few grains could hardly be seen. But by the time he’d got to the 16th square, he was already needing another kilogram of rice. By the 20th square, his servants had to bring in…

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