−1 3 22 61 125 219 348 original sequence 4 19 39 64 94 129 first differences 15 20 25 30 35 second differences 5 5 5 5 constant third difference
There is the constant difference you need. Continue that common difference for one more step:−1 3 22 61 125 219 348 4 19 39 64 94 129 15 20 25 30 35 5 5 5 5 5
Then work back up the array to find the next term of the sequence.−1 3 22 61 125 219 348 517 4 19 39 64 94 129 169 15 20 25 30 35 40 5 5 5 5 5
The next term in the sequence is 517.