There seems to be no logical order to this set of numbers.
* * * * *
Or, you could try 78.
Fit the quartic polynomial
t(n) = (7n4 - 66n3 + 221n2 - 186n + 216)/24 for n = 1, 2, 3, ...
18
108
29, assuming it is an algebraically reclusive sequence.
18-the correct number should be 20.
Well, darling, it looks like we're playing the guessing game. The next number is 15. How did I figure that out, you ask? Well, I just added the differences between each number and found the pattern. Easy peasy lemon squeezy.
21
24
24, they are going up in 3's, 13, 16, 19 and 18, 21 so next number is 24.
13 18 16 21 19 24 22 27 25 ... . This series consists of adding 5 to the first number and subtracting 2 from the next number, repeating the sequence in that order.
3 The series is obtained by subtracting a number that reduces by 1 at each stage 18 - 5 = 13 13 - 4 = 9 9 - 3 = 6 6 - 2 = 4 4 - 1 = 3
18
24 for each number you add 5 and then subtract 2. 19 plus 5 is 24.
The next number in the series 4, 12, 6, 12, 36, 18, 36
Since the numbers are going down be 5,4,3,2, the next number would be 3. It would be 3 because it would then go down by one.
The next number in the series 4-12-6-12-36-18-36.. is 108.
53
18