COPTIC NUMERICAL SYSTEM
When Copts adopted, at an early date, the Greek alphabet, they also abandoned the demotic numerals for the Greek system based on the principle of attaching a numerical value to letters of the alphabet. Thus in Coptic, numbers could be represented by the ordinary Greek alphabet together with additional letters which the Greeks had already borrowed from the archaic Phoenician alphabet and inserted in their own namely, the digamma (from Semitic waw) for 6, the koppa (from Semitic qof) for 90, and the san (from Semitic sadé) for 900. These twenty-seven letters represented the three series of nine numerals, the units, the tens, and the hundreds, and enabled the scribe to write the numbers from 1 to 999. The Greek supralinear diacritical mark was rendered in the regular Coptic script by a horizontal supralinear stroke.
The same letters marked with two parallel supralinear strokes were used as numerals for the thousands. This laborious detail seems to have been the reason for other forms in which the two supralinear strokes were replaced by one sublinear stroke, and also why all strokes were abandoned in several other examples.
Nonetheless, if these regular numerals suited quite a few Coptic manuscripts written in uncials, they were in fact less practical for rapid notations than the tailed Greek forms. This is why Greek numerals were often used in Coptic accounts rather than Coptic ones.
These regular numerals underwent a process of graphic transformation, observed in other scripts and in particular in hieratic and in demotic, yielding many paleographical variations, which are yet to be studied. It seems that at a later stage scribes tried to assimilate the three Semitic letters to Coptic characters, which were drawn from demotic. The koppa was finally standardized as a fay (f), the sadé as a shay (s) or as the barred Greek letter rho (r), while the digamma was never assimilated by the demotic sign for 6.
All these Coptic numerals were extensively used in Bohairic, less in Fayyumic, but rarely in Sahidic where numbers were normally written out in words. To express fractions, multiplication, and distributive concepts, Coptic terms were used in both Sahidic and Bohairic.