Maybe it is easier to define what isn't AI? Toshiba's handwritten postal code recognizers from the 1970s? Fuzzy logic in washing machines that adjusts the pre-programmed cycle based on laundry weight and dirtyness?
Historically, we often call something AI while we don’t really understand how it works. After that it quietly gets subsumed into machine learning or another area and called X algorithm.
Adding two numbers, each having 100 digits? Reciting the fractional part of Π on and on? I have only seen that done by talented people appearing in TV shows. Seems AI.