CONCORRENTI. – Conventional figures used by computists to determine which day of the week corresponds to the beginning of each year, and hence to establish when Easter falls.
The figure of the c., also called “solar epacts” or “greater epacts,” when referred to a given year, indicates how many days have elapsed between the last Sunday of the preceding year and the beginning of the new year. Since Easter is regulated by the spring equinox, the relationship between the c. and 24 March has been calculated: bearing in mind that from the beginning of the year to that date there are 82 days (83 in leap years), that is, 11 times 7, plus 5 days, 24 March will fall on a day of the week shifted by 5 units from that of 1 January; in other words, if in a given year 1 January falls on a Sunday, 24 March will fall on a Friday, and so forth. And since the dominical letters (v. LETTERA DOMENICALE) correspond to the c. as follows: A=6, B=5, C=4, D=3, E=2, F=1, G=7, the relationship between the c. and the day of the week on which 24 March falls is as follows:
| Concorrenti | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| dominical letter | F | E | D | C | B | A | G |
| day of the week on 1 January | Tues. | Wed. | Thurs. | Fri. | Sat. | Sun. | Mon. |
| and on 24 March | Sun. | Mon. | Tues. | Wed. | Thurs. | Fri. | Sat. |
In leap years, the figure of the c. naturally advances by one unit on 29 February.