The other tutor is exactly correct -- you can put any number next and it will be a valid sequence. So there is NEVER any way to know the "right" answer to any problem like this.
But it can be good exercise to spend a short time seeing if you can see a logical pattern in the numbers. A good problem like this will have a pattern that is relatively simple.
In this sequence, from one number to the next I see a big jump, then a little one, then another big one, another little one, and last another big one. That suggests to me multiplication where there is a big jump and addition where there is a small one.
Can you see a logical pattern like that with the given numbers?
The next jump should be a small one.... Answer by TeachMath(96) (Show Source): You can put this solution on YOUR website! a1: 20
a2: a1 * 2 = 40
a3: a2 + 3 = 40 + 3 = 43
a4: a3 * 4 = 43(4) = 172
a5: a4 + 5 = 172 + 5 = 177
a6: a5 * 6 = 177(6) = 1,062
a7: a6 + 7 = 1,062 + 7 = 1,069