If 1 = 0, 3 = 6, 4 = 12, 2 = 2 then 5 = ?

Question

If possible fill + or - for o and make this true, if not possible then provide the reasoning...

1 o 1/2 o 1/3 o 1/4 o 1/5 o 1/6 o 1/7 o 1/8 o 1/9 o 1/10 o 1/11 o 1/12 = 0

Answer 1

square the number and then deduct the number,hence (5x5)-5=20 which is the answer

Comments

also n(n-1) so 5*4