The keypad on my friend's microwave is broken: only one of the number keys (the N key) works. He found a workaround that allows him to cook for exactly 2 minutes, which is perfect for rewarming his giant cup of coffee. He does this by entering NN seconds, then start. He cooks for a period of time and then hits the pause button followed by N and start. (On his microwave, entering 99 would be the same as entering 139, since the 3rd number from the right is minutes)

For example, if N were "1", he could enter 11, cook until the display reads 6, pause, enter 1 (the display then reads 61), and cook for a total of 66 seconds. He also brags that using the same N key as above, but by pausing at a different time, he can cook for another whole number of minutes (other than 2).

Which number key is working on his microwave?