What is 'a 20 50'?

Once upon a time in a land called Reno, when my oldest niece was young, we always played the 'I love you' game. Here is how it went:

Me: I love you
Her: I love you, too.
Me: I love you three.
Her: I love you four.
Me: I love you five.
Her: I love you like a hundred.
Me: I love you like a million.
Her: I love you like a 20 50.
Me: I love you like a 20 51.
Her: No! It only goes to 20 50. That's the highest number.