There is a column of numbers a1a2a3. An. Starting from the second number, each number is equal to the difference between one and the reciprocal of the number in front of him. If A1 equals two, what is a2007

There is a column of numbers a1a2a3. An. Starting from the second number, each number is equal to the difference between one and the reciprocal of the number in front of him. If A1 equals two, what is a2007

a1=2,a2=1/2,a3=-1,a4=2,a5=1/2,a6=-1.
Therefore, this sequence is a cyclic sequence with a period of 3
a2012=a1

2, 3, 9, 18, 45, 99, what's the question mark

（99-45）/18=3
（45-18）/9=3
（18-9）/3=3
therefore
（X-99）/45=3
X=234

Line 1 1 ` 4 ` 5 ` 10 Line 2 4 ` 8 ` 10 ` 12 line 3 9 ` 12 ` 15 ` 14
…… Column 1 column 2 column 3 column 4
Line 1 1 4 5 10
Line 2 4 8 10 12
Line 3 9 12 15 14
…… * * * *
81 in which row and column?
What row and column is 100 in?

It is found that the number of the nth row in the first column is n ^ 2 100 = 10 ^ 2, so the number of the nth row in the second column is 4N 100 = 4 × 25, so the number of the nth row in the third column is 5N 100 = 5 × 20