Canadian SIN Checksum Checker - Apex Method

IsCanadianSIN.cls

// Canadian SIN Checksum Checker
// Source: https://stackoverflow.com/questions/4263398/how-do-i-check-the-validity-of-the-canadian-social-insurance-number-in-c
@AuraEnabled(cacheable=true)
public static boolean IsCanadianSIN(string sSIN){

    Integer iChecksum = 0;
    Integer iDigit = 0;

    // Checking if number is not starting with 9
    if(!sSIN.startsWith('9')){
        for (Integer i = 0; i < sSIN.length(); i++){
            // even number else odd
            if ((Math.Mod((i+1),2)) == 0){
                iDigit = Integer.Valueof(sSIN.Substring(i, 1))*2;
                iChecksum += (iDigit < 10) ? iDigit : iDigit - 9;
            } else {
                iChecksum += Integer.Valueof(sSIN.Substring(i, 1));
            }
        }

        if(Math.Mod(iChecksum,10) == 0){
            return true;
        } else {
            return false;
        }

    } else {
        return false;
    }
}