Observe the law of the following numbers and fill in the blanks: 0,3,8,15,24 ··, then what is its 2005 number? What is the nth number?

0 = 1*1 - 1
3 = 2*2 - 1
8 = 3*3 - 1
15 = 4*4 - 1
24 = 5*5 - 1
Then its number of 2005 = 2005 * 2005 - 1 = 4020024
The nth number is = n ^ 2 - 1
(^ 2 for square)

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