What number is missing 3 6 12 6 12 24 18?

The missing number in the sequence is 36. The pattern alternates between multiplying the previous number by 2 and then adding 6, as seen in the progression: 3 (×2) = 6, 6 (×2) = 12, 12 (×2) = 24, and 24 (×1.5) = 36. Following that, 18 (×2) would be the next logical number after 36.