The third number in the twentieth line -1 2 -3 4 -5 6 -7 8 -9 10 -11 12 -13 14 -15 16 Find the third number on the twentieth line

You can see that the odd number is negative and the even number is positive,
The sign is removed,
Then there is one number in the first row, three numbers in the second row, and so on
Bring in n = 20. You can see that there are 39 numbers in line 20
1+3++5+7+.+37=（1+37）*19/2=361；
361 + 3 = 364, so it's 364

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