It’s a sequence of numbers where the next number is a fixed multiple of the previous one.

1 2 4 8 16 32 … Is a sequence with a ratio of 2.

96 48 24 12 6 3 … Is the sequence from the question with a ratio of 1/2. You see that elements 2 and 4 (counting from zero) sum to 30 and elements 3 and 5 sum to 15.

In general, the sequence can be expressed as a_k = c r^k for some starting value c and the ratio r.