Heh: when was the last time someone responded to one of NJAS's questions by saying the equivalent of "See A096237"? We (math-fun) discussed this in Feb-Mar 2003, eventually calling them "deletable primes," terminology which I think was preexisting. There seem to be infinitely many of them. At the time, we came across one surprising observation, which (in the way of the web) is still sitting here: http://people.brandeis.edu/~kleber/temp/deletable.html --Michael Kleber On 1/6/07, N. J. A. Sloane <njas@research.att.com> wrote:

Dear Funsters, The radio program Car Talk today was discussing the problem of finding the longest English word which has the property that you can repeatedly delete one letter and still have an English word, all the way until the empty word is left (the best solution mentioned had 11 letters).

At each step you can choose which letter to delete.

This led me to wonder about the analogous question for primes. This must be well-studied. What's the largest prime known with property that you can repeatedly delete a digit (you get to choose which digit) and still have a prime, all the way down to the empty word?

I don't want to sign this.

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