In this paper we have investigated the occurrence rate of high energetic(E>10
MeV) solar electron flares measured by IMP-8 spacecraft of NASA for solar cycle
21 (June, 1976 to August, 1986) first time by three different methods to detect
periodicities accurately. Power-spectrum analysis confirms a periodicity ~155
days which is in consistent with the result of Chowdhury and Ray (2006), that
"Rieger periodicity" was operated throughout the cycle 21 and it is independent
on the energy of the electron fluxes.Comment: 11 pages of PDF version of MSWORD, 3 figures with 1 tabl
