integrating exponential How can you integrate $\frac{e^{x-3}}{x^4} dx$.
I tried integration by parts but it's not possible.
Is some substitution possible ? 
I started off solving the diff eqn $(xy^2 + 3e^{x-3})dx - x^2ydy = 0$
It's a non-exact first order equation whose integrating factor is $1/x^4$.
Finally I got to the equation where I needed to integrate $\frac{e^{x-3}}{x^4} dx.$
But I can't seem to proceed.

I'm fairly sure that the integral of that doesn't have a closed form as your expression there seems very related to the Gamma function and the exponential integral.
