Almost perfect autocorrelation sequences

Almost perfect autocorrelation sequences are defined as complex periodic sequences such that all the out-of-phase autocorrelation coefficients are zero except one. The study is restricted to (-1,+1)-sequences. In this case, such sequences exist only if the period n is a multiple of 4. After setting up theoretical results, several sequences are constructed for every period n multiple of 4 in the range 8<or=n<or=100 except for six special values.<<ETX>>