Find largest left truncatable prime in a given base: Difference between revisions

=={{header|Maple}}==

<lang maple>MaxLeftTruncatablePrime := proc(b, $)

local i, j, c, p, sdprimes;

local tprimes := table();

sdprimes := select(isprime, [seq(1..b-1)]);

for p in sdprimes do

if assigned(tprimes[p]) then

next;

end if;

i := ilog[b](p)+1;

j := 1;

do

c := j*b^i + p;

if j >= b then

# we have tried all 1 digit extensions of p, add p to tprimes and move back 1 digit

tprimes[p] := p;

if i = 1 then

# if we are at the first digit, go to the next 1 digit prime

break;

end if;

i := i - 1;

j := 1;

p := p - iquo(p, b^i)*b^i;

elif assigned(tprimes[c]) then

j := j + 1;

elif isprime(c) then

p := c;

i := i + 1;

j := 1;

else

j := j+1;

end if;

end do;

end do;

return max(indices(tprimes, 'nolist'));

end proc;</lang>