Editing Doomsday rule (section)

=== Nakai's Formula ===
Another method for calculating the Doomsday was proposed by H. Nakai in 2023.<ref>{{Cite journal |last=Nakai |first=Hirofumi |date=2023-06-01 |title=A Simple Formula for Doomsday |url=https://link.springer.com/article/10.1007/s00283-022-10229-3 |journal=The Mathematical Intelligencer |language=en |volume=45 |issue=2 |pages=131–132 |doi=10.1007/s00283-022-10229-3 |issn=1866-7414|doi-access=free }}</ref> 

As above, let the year number ''n'' be expressed as <math>n=100c+y</math>, where <math>c</math> and <math>y</math> represent the century and the last two digits of the year, respectively. If <math>c_2</math> and <math>y_2</math> denote the remainders when <math>c</math> and <math>y</math> are divided by 4, respectively, then the number representing the day of the week for the Doomsday is given by the remainder <math>5(c_{2}+y_{2}-1)+10y \quad\text{mod}\; (7)</math>.

==== Example ====
(August 7, 1966)  The remainder on dividing <math>(c,y)=(19,66)</math> by 4 is <math>(c_2,y_2)=(3,2)</math>, which gives <math>5 \cdot (3+2-1)=20 \equiv 6</math>; 10 times <math>y</math> is <math>10 \cdot 66 = 660 \equiv {2}</math>, so Doomsday for 1966 is <math>6+2=8 \equiv 1</math>, that is, Monday. The difference between 7 and the Doomsday in August (namely 8) is <math>7-8=-1 \equiv 6</math>, so the answer is <math>1+6 = 7 \equiv 0</math>, Sunday.<ref>{{Cite web |last=thatsmaths |date=2023-06-22 |title=A Simple Formula for the Weekday |url=https://thatsmaths.com/2023/06/22/a-simple-formula-for-the-weekday/ |access-date=2025-03-21 |website=ThatsMaths |language=en}}</ref>