Number Series Questions

The series follow the rule,

21 = 
77 = 92-4
165 = 132-4
285 = 172-4

5,9,13,17,21,(+4)...
In the same way next no. will be
212-4 = 441 - 4 = 437

As per the BODMAS rule, Addition and subtraction can be treated on same priority (from left to right) when they are in consecutive order. 600 + (300/15) = ? × 31 600 + 20 = ? × 31 ? = 620/31 = 20

Here the series of the form is x2 - 1, x2 - 2, x2 - 3,...

 53 x 2 - 4 = 106 - 4 = 102

Here the number follows the given rule 

 $$\begin{gathered} 23-1, 33-1, 43-1, 53-1, ... \\ \end{gathered}$$

But 28 has been given in problem series.

so 28 is wrong number.

The given sequence is a combination of three series:
i)1st, 4th, 7th terms i.e, 2, 4, 9
ii)2nd, 5th, 8th terms i.e, 3, 6, 12
iii)3rd, 6th, 9th terms i.e, 4, 8, 16
In each one of i, ii, iii, each term is twice the preceding term.
So, 9 is wrong and must be replaced by (4*2) = 8

Take a Look at the below sereies

2×1+12=3

3×2+22=10

10×3+32=39

39×4+42=172

172×5+52=885

Here 2nd number = (1st number x 1 )+1

 3rd number = (2nd number x 2 +2) 

4th number = (3rd number x 3 )+3 and so on..

Therefore, 5th number = (4th number x 4) +4 =57 x 4 + 4 =232.

Clearly, the numerators of the fractions in the given sequence follow the series of 2, 3, 5, 7,... and the denominator follows 3, 9, 27, 81, 243, ...
Then, the next term in the given sequence is  935 = 9243 = 127 .