What should come next in the following number series?
9 8 7 6 1 2 3 4 5 9 8 7 1 2 3 4 5 9 8 7 1 2 3 4 9 8

9 7 5 3 1 1/ 8 6 4 2 2/ 9 7 5 3 1/ 8 6 4 2 2 / 9 7 5 3 1/ 8 6 4 2/ 9 7 5 3/ 8 6 4 2

From given figure , it is clear that the increasing order of series given as -
First term = 0
Second term = First term + 5
? Second term = 0 + 5 = 5
Third term = Second term + 55
? Third term = 5 + 55 = 60
Similarly , we can find all others terms also.
Fourth term = Third term + 555
? Fourth term = 60 + 555 = 615
Fifth term = Fourth term + 5555
? Fifth term = 615 + 5555 = ?
? Fifth term ( ? ) = 6170

According to position of alphabets in alphabet table , we have
B C F G ? 2 , 3 ,6 , 7
J K N O ? 10 , 11 , 14 , 15
R S V W ? 18 , 19 , 22 , 23
{ ? Next sequence = Adding 8 in every position of previous sequence alphabets }
Next sequence = 18 + 8 , 19 + 8 , 22 + 8 , 23 + 8
Next sequence = 26, 27, 30, 31 = 26, 27 - 26 = 1, 30 - 26 = 4, 31 - 26 = 5 = Z A D E ( subtract the excess value by 26 )
We get , 26 , 1 , 4 , 5 ? Z A D E = ( ? ) .

See the graph and found that the given number in the series with specific pattern.
From the given graph , we can see that the increasing order of series as -
First term = 2
Second term = First term + 1 = 2 + 1 = 3 ,
Third term = Second term x 2 = 3 x 2 = 6 ,
Fourth term = Third term + 1 = 6 + 1 = 7 ,
Fifth term = Fourth term x 2 = 7 x 2 = 14 ,
Sixth term = Fifth term + 1 = 14 + 1 = 15 ,
Seventh term = Sixth term x 2 = 15 x 2 = 30
? Seventh term( ? ) = 30

See the below image and you will find a pattern in which numbers are getting added for next number in the given series.
From the given figure , we get the value of sixth term ( ? ) = 69

The pattern of the number series is as given below ;
8 + 2 = 10
10 + 8 (= 2 x 3 + 2) = 18
18 + 26(= 3 x 8 + 2) = 44
44 + 80 (= 3 x 26 + 2) = 124
124 + 424 (= 3 x 80 + 2) = 366

The pattern of the number series is as given below:

13 + 1 x 12 = 13 + 12 = 25
25 + 3 x 12 = 25 + 36 = 61
61 + 5 x 12 = 61 + 60 = 121
121 + 7 x 12 = 121 + 84 = 205
205 + 9 x 12 = 205 + 108 313

The pattern of the number series is given as follows:
454 + 18 = 472
472 - 27 = 445
445 + 18 = 463
463 - 27 = 436
436 + 18 = 454

The pattern of the number series is given as follows:
12 x 4 - 30 = 48 - 30 = 18
18 x 4 - 36 = 72 - 36 = 36
36 x 4 - 42 = 144 - 42 = 102
102 x 4 - 48 = 408 - 48 = 360
360 x 4 - 54 = 1440 - 54 = 1386

The pattern of number series is as follows :
7 x 2 - 2 = 12
12 x 4 - (2 + 6) = 48 - 8 = 40
40 x 6 - (8 + 10) = 240 - 18 = 222
222 x 8 - (18 + 14) = 1776 - 32 = 1744 ? 1742
1744 x 10 - (32 + 18) = 17440-50=17390