for (int i = 1; i <= N; i++) {
                        factorial = factorial * i;
                        if (!flagFirstEl) {
                            resultSum = factorial / Math.pow((x + i), 3);
                            firstElement = resultSum;
                            flagFirstEl = true;
                            dfm.addElement("a[" + i + "] = " + Double.toString(resultSum));
                            list1.setModel(dfm);

                        } else {
                            double sign = (Math.pow(-1, i - 1));
                            a = sign * (factorial / Math.pow((x + i), 3));
                            resultSum = resultSum + a;
                            nextElement = a;
                            if (Math.abs(nextElement) > Math.abs(firstElement)) {
                                checkSeries = false;
                            }
                            firstElement = nextElement;
                            dfm.addElement("a[" + i + "] = " + Double.toString(a));
                            list1.setModel(dfm);

                        }

                    }
                    resultSum = new BigDecimal(resultSum).setScale(M, RoundingMode.UP).doubleValue();
                    textField3.setText(Double.toString(resultSum));
                    if (checkSeries)
                        dfm.addElement("Series converges");
                    else
                        dfm.addElement("Series diverges");