Finds the missing number in a list

FindMissingNumberInList

//Find the missing number in a list
//http://stackoverflow.com/questions/2113795/quickest-way-to-find-missing-number-in-an-array-of-numbers
//list can start anywhere, assumes arithmetric series where n, n+1,n+2 etc.. 

function getMissingNum() {
    var start = Math.floor(Math.random() * 150) / 1;
    var nElem = Math.floor(Math.random() * 20) / 1;
    var set = [];
    var rand = Math.floor(Math.random() * nElem) + start / 1;
    for (var i = start; i <= start + nElem; i++) {
        //skip one number randomly
        if (i == rand) continue;
        set.push(i);
    }

    var sum = 0;
    for (var i = 0; i < set.length; i++) {
        sum += set[i];
    }

    // Total = N * (N + 1) / 2
    var max = set[set.length - 1];
    var min = set[0];// - 1;
    var actual = (((max * (max + 1)) / 2));
    var excluded = (((min * (min + 1)) / 2));
    var missing = actual - excluded - sum + start;
    if (min > start) {
        missing = missing + min;
    }
    return {
        missing: missing,
        min: min,
        max: max,
        actual: actual,
        excluded: excluded,
        rand: rand,
        start: start,
        nElem: nElem
    }
}

var results = [];
for (var i = 0; i < 100; i++) {
    var result = getMissingNum();
    if (result.rand != result.missing) {
        results.push(result);
    }
}