There is no formula, but I can point out that:
between the numbers you get:
+1,+2,+3,+4+5... so the next term would be +6 or 21
5
15(1)
5
The next figure would be 21, followed by 11 & 10.
5+5 = 10 10+5 = 15 15-5 = 15 10+5 = 15
5
5
15
the answer should be 5
20, 15, 10, 5, 0, -5, -10, -15, -20 and so on.
10
75The number which best completes the sequence 10 30 15 16 48 24 25 is 75.