Regex using angularjs ng-pattern

Question

I want to use angularjs ng-pattern.

Wich regex can i, using four characters, to allow the first just being a number, the second being a number OR a letter, the third being only a number and the fourth being only a number.

I try this one but it only allows letters on the second character.

[0-9]{1}[A-Z]{1}[0-9]{2}$