Dolphins most probably are sentient, and we still can't communicate with them well enough to talk about arithmetic.
Even if some animals can figure out small numbers, anything over 7 is just too much for them.
To have an algorithm to sum any arbitrarily pair of huge numbers, that's entirely something else, even for many people.
Any other 'thing' that's sentient being able to generalize sums is just speculation on your part.
Dolphins most probably are sentient, and we still can't communicate with them well enough to talk about arithmetic.
Even if some animals can figure out small numbers, anything over 7 is just too much for them.
To have an algorithm to sum any arbitrarily pair of huge numbers, that's entirely something else, even for many people.
Any other 'thing' that's sentient being able to generalize sums is just speculation on your part.