3n^2-n=1,
6n^3+7n^2-5n+2003
=6n^3-2n^2+9n^2-5n+2003
=2n(3n^2-n)+9n^2-5n+2003
=2n*1+9n^2-5n+2003
=9n^2-3n+2003
=3(3n^2-n)+2003
=3*1+2003
=2006