No 35

A Prime Rich Decade

In the decade 1990-1999 three of the years were prime:

1993 , 1997 and this year 1999.

Since all primes other than 2 and 5 end in either 1, 3, 7 or 9 then this decade has been RICH in primes.

The most prime years possible in a decade is four. The last such VERY RICH decade was 1800-1899:

1801, 1803, 1807 and 1809 are all prime.

An amazing fact is that there has been no VERY RICH decade for one hundred years.

In fact the current RICH decade is the first since 1780-1789:

1783, 1787 and 1789 are all prime.

So how long do you have to wait until the next RICH or VERY RICH decade? Will it be in your lifetime?

The good news is that if you are of school age just now you may just experience the next VERY RICH decade.

However the bad news is that you will definitely not experience another RICH decade like the present one.

So when are they? Search for yourself in the The Prime List.

If you have answers, discoveries, new questions etc to do with this Number Fact then...

E-mail us at madrascollege.maths@fife.gov.uk

...and we will publish them here.

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