26 - 6 = 20

20 - 5 = 15

15 - 4 = 11

11 - 3 = 8

8 - 2 = 6

6 - 1 = 5

Therefore, 16 is wrong number.

The pattern is x1+3, x 2, x1+3, x 3, x1+3, x 4

The next number=60x4=240

The correct pattern is *2+1
So, 39 is wrong and must be replaced by (15 * 2 + 1) = 31

The given sequence is a combination of two series:
i.)Y,T, O and ii.)B, G, ?
i. consists of 2nd, 7th, 12th letters from end of English alphabet,while
ii. consists of 2nd, 7th, 12th letters from beginning of English alphabet
So, the missing letter in ii.) is the 12th letter from the beginning of English alphabet,which is L.

The first letter moves 3 steps forward. The second and third letters move 2 steps forward.

There is a gap of four letters between the first and second, the second and third letters.
There is a gap of four letters between the last letter and the first letter of the next term.

Here the letter series is alternative reverse order series. So we get P, N.

3 x 3 x 3 = 27 - 3 = 24

4 x 4 x 4 = 64 - 4 = 60

5 x 5 x 5 = 125 - 5 = 120

6 x 6 x 6 = 216 - 6 = 210

7 x 7 x 7 = 343 - 7 = 336

The given series is 1, 2, 6, 21, 88, ?

1

1 x 1 + 1 = 2

2 x 2 + 2 = 6

6 x 3 + 3 = 21

21 x 4 + 4 = 88

88 x 5 + 5 = 445

Hence, the next number in the given number sequence is 445.

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   9 3 5 = 9 243 = 1 27 .