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Truncatable primes: Difference between revisions
Added a solution in Maple
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Line 1,647:
n = PrimePi[1000000]; While[Not[RightTruncatablePrimeQ[Prime[n]]], n--]; Prime[n]
-> 739399</pre>
=={{header|Maple}}==
<lang Maple>
MaxTruncatablePrime := proc({left::truefalse:=FAIL, right::truefalse:=FAIL}, $)
local i, j, c, p, b, n, sdprimes, dir;
local tprimes := table();
if left = true and right = true then
error "invalid input";
elif right = true then
dir := "right";
else
dir := "left";
end if;
b := 10;
n := 6;
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;
while p < b^n do
if dir = "left" then
c := j*b^i + p;
else
c := p*b + j;
end if;
if j >= b or c > b^n 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;
if dir = "left" then
p := p - iquo(p, b^i)*b^i;
else
p := iquo(p, b);
end if;
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>
<pre>
> MaxTruncatablePrime(right); MaxTruncatablePrime(left);
739399
998443
</pre>
=={{header|MATLAB}}==
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