  Studies on the periodic variation and the phase relationship between
different solar activity indicators are useful for understanding the long-term
evolution of solar activity cycle. Here we report the statistical analysis of
grouped solar flare (GSF) and sunspot number (SN) during the time interval from
January 1965 to March 2009. We find that, 1) the significant periodicities of
both GSF and SN are related to the differential rotation periodicity, the
quasi-biennial oscillation (QBO), and the eleven-year Schwabe cycle (ESC), but
the specific values are not absolutely identical; 2) the ESC signal of GSF lags
behind that of SN with an average of 7.8 months during the considered time
interval, implying that the systematic phase delays between GSF and SN
originate from the inter-solar-cycle signal. Our results may provide evidence
about the storage of magnetic energy in the corona.
