Number Series

13  25  61  121  205  ?

a) 323

b) 326

c) 324

d) 313

313

take double difference first 12,36,60,84 now you can clearly see the difference of is nos is 24 now add 24 in 84 you get 108 then add 108 to 205 you get your answer

take the difference, you will get odd multiples of 12 i.e 12, 36, 60 84 the next number will be 108+205=313

313

12*1

12*3

12*5

12*7

12*9