This is a combination of two alternating series. Series 1: 3, 7, 13, 21, 31 (increases by 4, 6, 8, 10). Series 2: 4, 7, 13, 22, 34 (increases by 3, 6, 9, 12). The next term belongs to Series 1 and is 31 + 12 = 43.