31
20
108
81
20
The series alternates between two patterns: one where numbers are multiplied by 3 and then reduced (18 to 27 to 36) and another where numbers are multiplied by 4 and then reduced (81 to 72 to 63). Following this pattern, the next number after 36 (from the first sequence) would be 45 (36 multiplied by 1.25), and after 63 (from the second sequence), the next number would be 54 (63 reduced by 9). Thus, the next number in the series is 45.
20
The next number in the series 4, 12, 6, 12, 36, 18, 36
The next number in the series 4-12-6-12-36-18-36.. is 108.
It is: 36 because 6 squared = 36
108
108
108
108
81
108
31
20