No. 42: Nov-Dec 1985
The following is also an abstract from the publication Cycles.
"An analysis of the mean annual sunspot numbers is made with particular emphasis on cycles have periodicities near 21 years. The results are compared not only with the original sunspot data but also with long-term geomagnetic and economic data. It is concluded that the '11-year' solar cycle periodicity increased during the 19th century, during which time there were only 8 peaks when 9 might have been expected. Doubt is cast on the reality of a 22-year sunspot cycle during the past three centuries, and the likelihood is shown that the reliable 21.2-year sunspot cycle is also the Hale magnetic cycle and that several of its harmonics are present in the economic data."
(Robbins, Roger W.; "The Case of the Missing Sunspot Peak," Cycles, 36:53, 1985.)