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
