>>121
log(x^2+1)=log(x+i)+log(x-i)
これを積分して
(x+i)log(x+i)-(x+i)+(x-i)log(x-i)-(x-i)
=xlog(x^2+1)+ilog((x+i)/(x-i))-2x
=xlog(x^2+1)+2iarctan x - 2x