9-3 = 6
21-9 = 12
46-21 = 25
91-46 = 45
163-91 = 72
269-163 = 106
Now check the difference between those differences (second differences).
12-6 = 6
25-12 = 13
45-25 = 20
72-45 = 27
106-72 = 34
Notice that the second difference increases by 7 each time. So the next second difference is 41. 106+41=147. 269+147=416, the next number in the sequence.
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