Ramanujan Theta Function is a special math function named after an Indian mathematician named Srinivasa Ramanujan.
Think of it like a magic equation that when you put some special numbers into it, it gives you a really interesting answer. The special numbers are the digits of the counting numbers. For example, when you put the digit of 1, 2, 3, and 4 into the function, it gives you a different answer than if you put the digit of 5, 6, 7, and 8.
The Ramanujan Theta Function can help us understand a lot of things like how many ways you can make change for a specific amount of money or how many ways you can write a number as a sum of squares.
It's like a cool trick that helps us solve some big puzzles.