Easter

Algorithm for calculating the date of Orthodox Easter

a=Y%4;
b=Y%7;
c=Y%19;
d=(19*c+15)%30;
e=(2*a+4*b-d+34)%7;
f=3+(d+e+21)/31;
g=(d+e+21)%31;
month=f;
day=g+1;

Algorithm for calculating the date of Catholic Easter

G=[Y%19]+1 (G - gold number in the metonic cycle);
C=[Y/100]+1 (if Y is not a multiple of 100, then C is the century number);
X=[3·C/4]-12] (correction for the fact that three of the four year-folds are not 100 leagues;
Z=[(8·C+5)/25]-5] (synchronization with the lunar orbit, year is not a multiple of the lunar month);
D=[5·Y/4]-X-10 (in March, the day? D mod 7 will be Sunday);
E=[(11·G+20+Z-X)%30] (ground or epact - indicates the day of the full moon);
If (E=24) or (E=25 AND G>11) then increase E by 1;
N=44-E (N March is the day of the calendar full moon);
If N < 21 then increase N by 30;
N=N+7-[(D+N)%7];
If N > 31 then the date of Easter (N-31) April is otherwise the Easter date of March N.