Interesting! Now what is the J verb that will find an n-digit integer that is still prime when each of the digits are removed?
Skip Cave Cave Consulting LLC On Sat, Nov 19, 2022 at 3:51 PM Richard Donovan <rsdono...@hotmail.com> wrote: > Hi > > I am doing experiments with large primes, in particular looking at primes > that remain primes when n digits are truncated from the left. For example > 6391373 391373 91373 1373 373 73 3 remains prime at each > step. > > The largest of these in base 10 is 357686312646216567629137. > > I wrote the following code in preparation for further investigation but I > find that the 24 digit number above is not handled as I wish it to be, as > you will see below. > > What have I missed? > > Thanks > > > > > digits > "."0@": > > ltrunc > 3 : 0"0 0 0 > n=: ": 0, }. digits y > x: ". n-. ' ' > ) > > > > NB. Works fine with 7 digit number... > ltrunc^:a: 6391373 > 6391373 391373 91373 1373 373 73 3 0 > > > NB. But I can’t get it working for a 24 digit number! > ltrunc 357686312646216567629137 > 0 0 5 7 6 8 6 0 2 3 > ltrunc 357686312646216567629137x > 57686312646216568012800 > ltrunc x:357686312646216567629137x > 57686312646216568012800 > > Is there a way around the limit? > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
