A (surely not THE) verb?:
(#~{{*/ (1 p:".) ry #~"1 -.=i.#ry =. ":y }}"0) range 100 200
111 113 117 119 131 137 171 173 179 197
Mike
On 19/11/2022 23:46, 'Skip Cave' via Programming wrote:
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?
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