In Microsoft Excel, the ^ symbol means exponents. For example, 4^3 means four to the third power (4 x 4 x 4 = 64). I assume that's what it means here, but it's not 100% clear without some further context.
I was a math major in college. The ^ symbol was not used in algebraic expressions back in the old days when math was done with pencil & paper. I believe the ^ symbol came about in the personal computer age.
By the way, I'd be curious to understand how any of this applies to images. If the image is any kind of normal photograph, then it's not obvious that a photogaph can be summarized down to one number, or what that would even mean. The only situation I can think of where this kind of thing applies in Photoshop is in layer blend modes, where mathematical operations are done to individual pixels on one layer that sit immediately above other pixels on other layers.
I should also add that if they followed proper precedence of operations, then that is important to get the answer. Here is a link with the proper accepted precedence order of various operators. It puts the bitwise EOR and lowest precedence under addition and multiplication. FYI: https://en.cppreference.com/w/c/language/operator_precedence