Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_45281 ( "Series Number" real, "Number of Episodes" real, "Original Air Date" real, "DVD Region 2 release date" text, "DVD Region 1 release date" text )

### Question ###
What's the sum of the number of episodes that originally aired after 1991 with a series number smaller than 21 and a DVD Region 2 release date of 26 march 2012?

### Accurate SQL ###

SELECT SUM("Number of Episodes") FROM table_45281 WHERE "Original Air Date" > '1991' AND "Series Number" < '21' AND "DVD Region 2 release date" = '26 march 2012'