If your @startvalue is for example 10, and you want to get 11,12,13 etc. do this:
CAST(@StartValue + Row_number() over (order by (select 1)) AS NVARCHAR(5));
If your @startvalue is for example 10, and you want to get 101,102,...109,1010,1011 etc., do this:
CAST(@StartValue AS NVARCHAR(5)) + CAST(Row_number() over (order by (select 1)) AS NVARCHAR(5));