Yesterday, I bought a new calculator in an antique shop. I wanted to try some basic operations to see if it was working well. Everything felt right, except for the + sign: it seemed like it was replaced with an obscure new operator!

At first, I tried these additions that seemed totally fine:

    5 + 5 = 10
    6 + 5 = 11
    39 + 8 = 47
    6 + 3 + 7 + 10 = 26

But then, things started to go slightly off with some additional tries:

    6 + 4 = 12
    7 + 3 + 10 = 21
    8 + 4 + 9 = 22

So I computed more operations, and nothing made sense anymore!

    2 + 2 = 10
    1 + 2 + 3 + 4 = 1
    5 + 5 + 5 + 5 + 5 = 130
    3000 + 333 + 30 + 3 = 1020

My last hope to try to understand this operator was to compute a random big number to understand what's going on, but all I got was: 

    17603415 + 33 = ERROR

So, can you tell me **what is this operator that replaced the + sign on my calculator?**