A little more detail.

1. Use an Execute SQL Task to retrieve the LastUsedNumber and store the result in a variable (let's call it @LastUsedNumber :). See this article on how to do that: Execute SQL Task.

2. Create a string variable called @SQLStatement. Put the EvaluateAsExpression property to true and enter the following expression for the value property:

"SELECT * from table1 WHERE recordnumber > " + (DT_STR,10,1252) @[User::LastUsedNumber]

3. In your OLE DB Source, choose the SQL command from variable option and pick the @SQLStatement variable.