Fig. 4


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The maximum annual number of spotless days in each inter-cycle interval vs. maximum annual sunspot number of the following solar cycle. Values for Solar Cycles 1–24 are shown as black plus signs. The solid line is a linear fit to the data and the blue “+” is the prediction that S 25 = 150 based on using a spotless day count of 273 in 2019 in that fit.

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