public static BigInteger randomVeletlen(){
        while(true){
            int c=(int)(Math.random()*(fn.intValue()-2))+2;
            BigInteger a=BigInteger.valueOf(c);
            if(euklidesziAlg(fn,a,n).compareTo(new BigInteger("1"))==0){
                return a;
            }
        }
    }

    public static BigInteger euklidesziAlg(BigInteger a, BigInteger b, BigInteger d){
        d = a;
        if (b.intValue() != 0){
            return euklidesziAlg(b, a.mod(b), d);
        }
        return d;
    }