I try to analyze the Wolf numbers. I have never analyzed time series before. Firsty I calculate autocorrelation coefficients. Biggest coefficients were for delays: 1, 2, 6, 7, 8, 9, 10. I calculated differences D(-1), D(-9). But for both calculated time series autocorrealtion coefficients for delays 1 and 9 were big and significant. My (first) question why it so? Is it normal situation?