if we give index number to each of the given number , our series will be :

index no - given no

1 - 17

2 - 27

3 - 44

4 - 64

5 - 108

6 - 138

now , through inspection we can say that difference between number with odd index with even index is multiple of 10 i.e. 27-17 = 10 , 64-44 = 20 , 138-108 = 30

&

difference between number of even index with odd index is previous number stored at odd index i.e.

44-27 = 17 (located at index 1) , 108-64 = 44 (located at index 3) .

hence , next number will be 138 + 108 = 246