n*(n+1) = 6*(n+(n+1)) - 36 n^2 + n = 12n + 6 - 36 n^2 - 11n + 30 = 0 (n-5)*(n-6) = 0 There are two roots: n= 5 and n= 6. CHECK for n= 5: 5*(5+1) = 5*6 = 30; 6*(5+6) - 36 = 6*11 - 36 = 66 - 36 = 30, the same number. ! Correct ! CHECK for n= 6: 6*(6+1) = 6*7 = 42; 6*(6+7) - 36 = 6*13 - 36 = 78 - 36 = 42, the same number. ! Correct ! ANSWER. The problem has TWO PAIRS of consecutive integer solutions: (5,6) and (6,7).