You know those people who can tell the day of the week for historical dates?

[DogwoodTree]

It's just math. It's knowing the patterns and doing the mental math.

Here's a link that explains how:

http://gmmentalgym.blogspot.com/2011/03/day-of-week-for-any-date-revised.html#ndatebasics

None of the math functions are difficult--it's easy to do in your head. The challenge is having all the right patterns in your head, and knowing all of the exceptions for dealing with leap years and different centuries and all that.

Anyway, I just spent a ridiculous amount of time learning how to do this, lol. That was fun.

 

[AGXStarseed]

I remember watching a program about Autism some time back (Uta Firth was narrating it) and it showed an Autistic boy who could do that and it showed him in his class taking 'date suggestions' from his classmates.
The look on their faces when he told them the day and they found out he was correct was hilarious.