Because we all want to count in base 42.

TetraHexaDecaunalInteger.java

import java.util.Arrays;
import java.util.List;

/**
 * @author zyuiop
 */
public class TetraHexaDecaunalInteger {
	private int[] factors;
	private List<Character> characters = Arrays.asList('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F');

	public TetraHexaDecaunalInteger(int... factors) {
		this.factors = factors;
	}

	public TetraHexaDecaunalInteger(TetraHexaDecaunalInteger integer) {
		this.factors = integer.factors;
	}

	public TetraHexaDecaunalInteger(String tetraHexaString) {
		if (tetraHexaString.startsWith("~"))
			tetraHexaString = tetraHexaString.substring(1);

		int[] factors = new int[tetraHexaString.length()];
		int i = 0;
		for (char c : tetraHexaString.toCharArray()) {
			factors[i] = characters.indexOf(c);
			i++;
		}

		this.factors = factors;
	}

	public Integer toInteger() {
		int value = 0;
		int maxPower = factors.length - 1;
		for (int i = maxPower; i >= 0; i--) {
			value += Math.pow(42, i) * factors[maxPower - i];
		}

		return value;
	}

	public static TetraHexaDecaunalInteger fromDecimal(Long decimalValue) {
		return new TetraHexaDecaunalInteger(toFactors(decimalValue));
	}

	/**
	 * Returns all the factors of 42 powers
	 * For example, the number 45 will return the following array :
	 * [1, 3]
	 * Because it can be written 1 * 42^1 + 3 * 42^0
 	 * @return An array of ints
	 */
	public static int[] toFactors(long decimalValue) {
		int maxPow = getMaxPower(decimalValue);
		int[] factors = new int[maxPow + 1];
		long value = decimalValue;

		for (int i = maxPow; i >= 0; i--) {
			long power = (long) Math.pow(42, i);
			int decimalResult = (int) Math.floorDiv(value, power);
			value -= (decimalResult * power);
			factors[maxPow - i] = decimalResult;
		}
		return factors;
	}

	private static int getMaxPower(long decimalValue) {
		int i = 0;
		while (Math.pow(42, i) <= decimalValue) {
			i++;
		}
		return (i >= 1 ? i-1 : 0);
	}

	public int[] getFactors() {
		return factors;
	}

	@Override
	public String toString() {
		StringBuilder builder = new StringBuilder();
		boolean first = true;
		int power = factors.length - 1;
		for (int factor : factors) {
			if (factor > 0) {
				if (!first)
					builder.append(" + ");
				builder.append(factor).append(" * 42^(").append(power).append(")");
			}

			if (first)
				first = false;

			power--;
		}

		return builder.toString();
	}

	public String toTetraHexaDecaunalString() {
		StringBuilder sb = new StringBuilder();
		for (int power : getFactors()) {
			sb.append(characters.get(power));
		}
		return "~" + sb.toString();
	}
}