[Gretl-users] ARIMA residual

Dear all: Afer estimating ARIMA, It is convenient to test if residual is white noise in Gretl. But I have two questions: 1. Gretl provide Ljung-Box Q statistic, residual acf and pacf. Some paper test lag of 1 to 24, Some only test lag of 6, 12, 18, 24. Some only test lag of 1, 12, 24. I am confused about the lag of Q statistic, acf and pacf. 2. Some paper test ARIMA residual by Q statistic, residual acf and pacf. But some just test by Q statistic. Ignoring residual acf and pacf. Are residual acf and pacf necessary when testing ARIMA residual ? Thanks a lot