2 × 4 = 5-1 3 × 5 = 4-1 4 × 6 = 5-1 11 × 13 = 12-1 find the nth formula

2 × 4 = 5-1 3 × 5 = 4-1 4 × 6 = 5-1 11 × 13 = 12-1 find the nth formula

(n+1)(n+3)=(n+2)^2-1