What is the 999th term of the series S ?

(1) The first 4 four terms of S are (1 + 1)² , (2 + 1)² , (3 + 1)² , and (4 + 1)².
(2) For every x, the xth term of S is (x + 1)².



From statement (1) - It is given that the 1st 4 four terms of S are (1 + 1)² , (2 + 1)² , (3 + 1)² , and (4 + 1)².

We only know the first four terms. We cannot assume that terms following the first 4 terms will be like -- nth term

= (n+1)^2.
There can be a sequence that follows a different rule for any term in it

From statement (2) - It is given that for every x, the xth term of S is (x + 1)². Hence sufficient as it implies

"for any number x that refers to the term in S."