Mathematical formula for permutation I have been assigned to write mathematical equation for permutation using only 1,3,5,7,9 numbers starting from single digit going up to five digits numbers. For example 
Single digit
1
3
5
7
9
two digit
1,3
1,5
1,7
1,9
Please note  3,1 is treated same as 1,3, or 1,1,3 is same as 1,3,1 and 3,1,1 
Thanks in Advance,
Rodney

The details will depend on the language you are supposed to use. Here is how it could be done in JavaScript: the numbers 1,3,5,7,9 are treated as letters; they get appended to existing strings (oldStrings) as long as this does not put letters out of alphabetical order (e.g., after 15 we cannot put 3 but can put another 5). So there is a triple loop here: one by length of string, one goes over existing strings, and one looks for letters to append, checking the alphabetization condition oldStrings[i].charAt(len-2)<=letters[j]
var letters = ['1','3','5','7','9'];
var oldStrings = [''];
var newStrings = [];
var answer = '';
for (var len=1; len<=letters.length; len++) {
    for (var i=0; i<oldStrings.length; i++) {
        for (var j=0; j<letters.length; j++) {
            if (oldStrings[i].charAt(len-2)<=letters[j]) { 
            newStrings.push(oldStrings[i]+letters[j]);
            }
        }
    }
    answer=answer+'Strings of length '+len+' are '+newStrings.join()+'\n';
    oldStrings = newStrings;
    newStrings = [];
}
alert(answer);​

This is not the most efficient code, but it works. Since this is your assignment, my advice is to re-think and redo the problem in another language (e.g., Python) as to avoid a charge of plagiarism.
