First of all, we must find the distribution law of wisdom numbers.

1. Because 2n+ 1=(n+ 1)? -n？ So all odd numbers except 1 are wisdom numbers (because 1= 1? -0? , and 0 is not a positive integer)

2. Because (n+2)? -n？ =4(n+ 1), so multiples of 4 are all wisdom numbers except 4.

Even numbers divided by 4 and divided by 2 are not smart numbers.

So the smallest wisdom number is 3, and the second wisdom number is 5. Starting from 5, it is 5, 7 and 8. 9, 1 1, 12; 13, 15, 16; 17, 19, 20。 . . That is, according to two odd numbers and multiples of 4, they are arranged in groups of three. According to this conclusion, we can easily know: 1999=3*666+ 1.

So 1999 wisdom number is 4(666+ 1)=2668.