Let the center of the circle be (n, 0), then the radius is the root sign (n 2+ 1).

The distance from the center of the circle to the straight line is |n+ 1|/ root number 2.

(|n+ 1|/ root 2) 2+ (root number 2) 2 = n 2+1.

n^2+2n+ 1+4=2n^2+2

n^2-2n-3=0

N=- 1 or 3 (exclusive)

(x+ 1)^2+y^2=2