I[n-1]∫dx/(x^2+1)^(n-1)
=∫(x^2+1)/(x^2+1)^n dx
=∫{x*(x^2+1)^(-n)}*x dx+∫dx/(x^2+1)^n
=1/(2n-2)*(x^2+1)^(-n+1)*x-∫dx/(2n-2)*(x^2+1)^(-n+1)+I[n]
=1/((2n-2)(x^2+1)^(n-1))-I[n-1]/(2n-2)+I[n]