P_cyc length versus stellar rotation period P_rot. The filled circles indicate the primary cycles and the empty circles the secondary cycles. The arrows indicate the stars for which the visual inspection of time series revealed P_cyc ≥ 3000 d. The continuous line, dashed line, and dotted line represent the Aa, Ab, and I sequences identified by Böhm-Vitense (2007), respectively. The dash-dotted line represents the locus where the ratio is equal to the ratio between the typical length of the Rieger cycle and the solar rotation period. The red asterisk indicates the solar Schwabe cycle; the green asterisk indicates the solar Rieger cycle.