## last Saturday... (maximin prime dates)

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• [ trivial but maybe fun ] Last Saturday may have been a special day in primedom. It may have been a maximin prime date. At least, using the American
Message 1 of 1 , Nov 2, 2001
[ trivial but maybe fun ]

Last Saturday may have been a special day in primedom.

It may have been a "maximin" prime date. At least, using the
American convention of putting the month first.

Definitions: For a date with month a and day b, define the
sequence N of all n>1 such that a*10^n+b is prime.

If N is not empty, choose the minimum n in the sequence.

Then, find the maximum over all dates of these minimal n.

The dates which yield these maxima will be called "American
maximin prime dates"

Unless N is nonempty for the 1st of October, the only American
maximin prime date is the 27th October. 10.10^n + 27 is prime for
n=82, but composite for n=2,3,4,...,81

If we similarly define "European maximin prime dates", with the
month coming at the end, then (unless N is nonempty for the 10th
of January), the only European maximin prime date is the 31st of
January.

31.10^n + 1 is prime for n=51, but composite for n=2,3,...,50.

Do these get into the prime curios pages?? :-)

Anyone whose birthday falls on (one of) these two dates??

This email is inspired by a thread that occurred around the 4th of
July.

Yours, Mike H...

Michael Hartley : Michael.Hartley@...