81 is a good continuation although, since the seqeunce continues forever, it cannot be said to be completion.
The rationale for 81 is
u(n) = (n4 - 13n3 + 74n2 - 122n + 66)/6 for n = 1 ,2, 3, ...
16
75The number which best completes the sequence 10 30 15 16 48 24 25 is 75.
7
75
75.
18
It is: 10-3 = 7
15
15.
4 5 6 7 8
A sequence never ends. The next number in this one is 7 .
17 19 20