Task: Find largest left truncatable prime in a given base
C: #include <stdio.h>
#include <gmp.h>

typedef unsigned long ulong;

ulong small_primes[] = {2,3,5,7,11,13,17,19,23,29,31,37,41,
			43,47,53,59,61,67,71,73,79,83,89,97};

#define MAX_STACK 128
mpz_t tens[MAX_STACK], value[MAX_STACK], answer;

ulong base, seen_depth;

void add_digit(ulong i)
{
	ulong d;
	for (d = 1; d < base; d++) {
		mpz_set(value[i], value[i-1]);
		mpz_addmul_ui(value[i], tens[i], d);
		if (!mpz_probab_prime_p(value[i], 1)) continue;

		if (i > seen_depth ||
			(i == seen_depth && mpz_cmp(value[i], answer) == 1))
		{
			if (!mpz_probab_prime_p(value[i], 50)) continue;

			mpz_set(answer, value[i]);
			seen_depth = i;
			gmp_fprintf(stderr, "\tb=%lu d=%2lu | %Zd\n", base, i, answer);
		}

		add_digit(i+1);
	}
}

void do_base()
{
	ulong i;
	mpz_set_ui(answer, 0);
	mpz_set_ui(tens[0], 1);
	for (i = 1; i < MAX_STACK; i++)
		mpz_mul_ui(tens[i], tens[i-1], base);

	for (seen_depth = i = 0; small_primes[i] < base; i++) {
		fprintf(stderr, "\tb=%lu digit %lu\n", base, small_primes[i]);
		mpz_set_ui(value[0], small_primes[i]);
		add_digit(1);
	}
	gmp_printf("%d: %Zd\n", base, answer);
}

int main(void)
{
	ulong i;
	for (i = 0; i < MAX_STACK; i++) {
		mpz_init_set_ui(tens[i], 0);
		mpz_init_set_ui(value[i], 0);
	}
	mpz_init_set_ui(answer, 0);

	for (base = 22; base < 30; base++) do_base();

	return 0;
}

Java: import java.math.BigInteger;
import java.util.*;

class LeftTruncatablePrime
{
  private static List<BigInteger> getNextLeftTruncatablePrimes(BigInteger n, int radix, int millerRabinCertainty)
  {
    List<BigInteger> probablePrimes = new ArrayList<BigInteger>();
    String baseString = n.equals(BigInteger.ZERO) ? "" : n.toString(radix);
    for (int i = 1; i < radix; i++)
    {
      BigInteger p = new BigInteger(Integer.toString(i, radix) + baseString, radix);
      if (p.isProbablePrime(millerRabinCertainty))
        probablePrimes.add(p);
    }
    return probablePrimes;
  }
  
  public static BigInteger getLargestLeftTruncatablePrime(int radix, int millerRabinCertainty)
  {
    List<BigInteger> lastList = null;
    List<BigInteger> list = getNextLeftTruncatablePrimes(BigInteger.ZERO, radix, millerRabinCertainty);
    while (!list.isEmpty())
    {
      lastList = list;
      list = new ArrayList<BigInteger>();
      for (BigInteger n : lastList)
        list.addAll(getNextLeftTruncatablePrimes(n, radix, millerRabinCertainty));
    }
    if (lastList == null)
      return null;
    Collections.sort(lastList);
    return lastList.get(lastList.size() - 1);
  }
  
  public static void main(String[] args)
  {
    if (args.length != 2) {
      System.err.println("There must be exactly two command line arguments.");
      return;
    }
    int maxRadix;
    try {
      maxRadix = Integer.parseInt(args[0]);
      if (maxRadix < 3) throw new NumberFormatException(); 
    } catch (NumberFormatException e) {
      System.err.println("Radix must be an integer greater than 2.");
      return;
    }
    int millerRabinCertainty;
    try {
      millerRabinCertainty = Integer.parseInt(args[1]);
    } catch (NumberFormatException e) {
      System.err.println("Miiller-Rabin Certainty must be an integer.");
      return;
    }  
    for (int radix = 3; radix <= maxRadix; radix++)
    {
      BigInteger largest = getLargestLeftTruncatablePrime(radix, millerRabinCertainty);
      System.out.print("n=" + radix + ": ");
      if (largest == null)
        System.out.println("No left-truncatable prime");
      else
        System.out.println(largest + " (in base " + radix + "): " + largest.toString(radix));
    }
  }
  
}