lol. there is no such thing as "the largest" number. i could always add 1 to whatever anyone in here can come up with to get a larger number, and then add some more to increase the value.
that's why the term 'infinite' exists -- denotes a quantity or set larger than any finite (limited in magnitude or spatial or temporal extent) number. so, to add 1 to infinity is will be no better than adding 2 to infinity, and so would adding infinity to infinity, the difference would only be the rate the numbers increase. there would still be and endless count.
so, again, to answer the question of what is the largest number - there is no such thing.