Number of spot groups formed and their average lifetime in solar activity cycle No. 20

The paper represents a sUpplement to the values published earlier of the number of sunspot groups formed and their average lifetime, in this case of the values for the 11-year cycle No. 20, i.e. for the years 1965 to 1976. It is shown that in cycle No. 20, the average lifetime of sunspot groups further decreased as compared to cycles Nos 19 and 18 and that the number of groups formed in cycle No. 20 proves the existence of a systematic increase in the number of sunspot groups formed over the last 100 years; this is probably associated with a solar activity variation of several hundred years and supports our forecast of an abnormally high solar activity for the next century. (author)