REPLICATE( N'A', 4000000));

what is the meaning of N in N'A'? is it the maximum length.

I executed the below statements,

INSERT #t VALUES (1, REPLICATE( N'A', 4000000));

INSERT #t VALUES (2, REPLICATE( 'A', 4000000));

SELECT DATALENGTH(LongName) FROM #t

The result of the SELECT is

8000

16000

I don't know why i got 16000. Can anyone explain me?