<Dd> y is...</Dd> <P> So, for example, if you want to find' y' for the year 1987: </P> <Dl> <Dd> y = (⌊ 87 4 ⌋ + 87) mod 7 = (21 + 87) mod 7 = 108 mod 7 = 3 (\ displaystyle (\ begin (aligned) y& = \ left (\ left \ lfloor (\ frac (87) (4)) \ right \ rfloor + 87 \ right) (\ bmod (7)) \ \ & = (21 + 87) (\ bmod (7)) \ \ & = 108 (\ bmod (7)) \ \ & = 3 \ \ \ end (aligned))) </Dd> </Dl> <Dd> y = (⌊ 87 4 ⌋ + 87) mod 7 = (21 + 87) mod 7 = 108 mod 7 = 3 (\ displaystyle (\ begin (aligned) y& = \ left (\ left \ lfloor (\ frac (87) (4)) \ right \ rfloor + 87 \ right) (\ bmod (7)) \ \ & = (21 + 87) (\ bmod (7)) \ \ & = 108 (\ bmod (7)) \ \ & = 3 \ \ \ end (aligned))) </Dd>

Formula for day of week based on date