This is quite a good problem. See if you study the gaps then:

Difference between 3 and 20 is 17, 20 and 63 is 43, 144 and 63 is 81and 275 and 144 is 131.

Now the difference are: 17,43,81,131. Now if you again find the difference between them then 43-17=26. Similary, 80-43=38, 131-81=50 Now again if we find the difference of this series then we will find that the gap is equal i.e., 12.

So our result will be 50+12=62, 62+131=193 =>275+193=468.

Thus the result will be 468.

I hope this answer help. All the very best for your future endeavors!