The pattern seems to involve multiplying the first number by an increasing factor, and then adding a constant. In the given series, the factor is 3 and the constant varies: (2 * 3) + 0 = 6, (6 * 3) + 2 = 20, (18 * 3) + 4 = 58, (4 * 3) + 8 = 20, (20 * 3) + 16 = 76. Following this pattern, the missing number should be (100 * 3) + 32 = 332. So, the complete series is 2, 6, 18, 4, 20, 100, 332, 21, 147.