Answer:
I think the common difference is 2. The formula to create the sequence is n (number) is multiplied by 2.
1 x 2 = 2
2 x 2 = 4
4 x 2 = 8
8 x 2 = 16
16 x 2 = 32
32 x 2 = 64
64 x 2 = 128
128 x 2 = 256
256 is the 8th term of the sequence. Since your question says that we should look for the sum, add the number of the sequence I guess.
2 + 4 +8 + 16 + 32 + 64 + 128 + 256 = 510
