Why is there a 21 gun salute? Rather than any other number? Why 21?

Answer 1

Well here is what the army has to say about it:

"In 1842, the Presidential salute was formally established at 21 guns. In 1890, regulations designated the "national salute" as 21 guns and redesignated the traditional Independence Day salute, the "Salute to the Union," equal to the number of states. Fifty guns are also fired on all military installations equipped to do so at the close of the day of the funeral of a President, ex-President, or President-elect."

Answer 2

21 is the sum of the numbers 1 7 7 6.... it's that simple.