In some form of another, you've probably heard of the hit game series Pokemon. Pokemon may seem like a simple game that requires little thought to get into. But, Pokemon is a game that requires you, the player, to calculate hundreds of mathematical equations in the first 5 minutes.
Right when you open up the game, players are forced to used math. You see, Pokemon's code bases its encounters based on the values in the player's name. Each letter of the player's name has a certain value that the game adds up and keeps in the back of its mind when you(the player) are walking around. This however took players who were crazy good at math to figure out and they had to dig around in the game's code to figure out the true values. Name yourself whatever you want, this doesn't matter too much.
Each area of the map has a certain number of Pokemon that can appear. For example, if you're playing Pokemon Red version, you can encounter the Pokemon Weedle, Caterpie, Kakuna, Metapod, and Pikachu. The Pokemon you will encounter most is Weedle, as it has a higher encounter rate. You might run into Caterpie, but it has lower encounter rate. This is actually different in Pokemon Red's counter part, Pokemon Blue, where the player has higher chance of running into a Caterpie. One Pokemon you that is rare to appearing is the Pokemon mascot, Pikachu. Unless you're going out of you're way, you probably won't ever find one.