It happens that I'm just starting to learn coding and I needed something similar as you have just asked in SQLite (I´m using [SQLiteStudio] (3.1.1)).
It happens that you must define the column's 'Constraint' as 'Not Null' then entering your desired definition using 'Default' 'Constraint' or it will not work (I don't know if this is an SQLite or the program requirment).
Here is the code I used:
CREATE TABLE <MY_TABLE> (
<MY_TABLE_KEY> INTEGER UNIQUE
PRIMARY KEY,
<MY_TABLE_SERIAL> TEXT DEFAULT (<MY_VALUE>)
NOT NULL
<THE_REST_COLUMNS>
);