4, 5, 7, 10, 14, 18, 25, 32?

2nd = (1st + 1) : 3rd = (2nd + 2); 4th = (3rd + 3); 5th = (4th +4).
But 18 = 6th term not equal ≠ 5th + 5 = 14 + 5 = 19.