A daily index of SUNSPOT activity (R), defined as R = k (10 g + s) where S = number of individual spots, g = number of sunspot groups, and k is an observatory factor (equal to 1 for the Zurich Observatory and adjusted for all other observatories to obtain approximately the same R number). The standard number, RI, once derived at Zurich (see Wolf number), is now being derived at Brussels and is denoted by RI. Often, the term "sunspot number" is used in reference to the widely distributed smoothed sunspot number.
ON-LINE GLOSSARY OF SOLAR-TERRESTRIAL TERMS of National Geophysics Data Center

This term is basically self-explanatory. It represents the number of observed sunspots and sunspot groups on the solar surface. It is computed according to the Wolf Sunspot Number formula: R = k (10g + s), where 'g' is the number of sunspot groups (regions), s is the total number of individual spots in all the groups, and k is a scaling factor that corrects for seeing conditions at various observatories. Sunspot number varies in phase with the solar flux.

Sunspot numbers can vary between zero (for sunspot minimum periods) to values in excess of 350 or 400 (in the very active "solar max" period of the suns 11 year cycle). Solar flux is related to the sunspot number, since sunspots produce radio emissions at 10.7 cm wavelengths (as well as at other wavelengths).

 Mr. Vaino K. Lehtoranta