Expansion of polynomial raised to high power Is there an easy way to expand something like (x + x^2 + x^3)^6 ?
Thanks in advance!

My approach avoids multinomials:
Let's play with it a bit:
$$\begin{align}
(x+x^2+x^3)^6 &= x^6(1+x+x^2)^6\\
&= x^6\frac{((1-x)(1+x+x^2))^6}{(1-x)^6}\\
&= \frac{x^6(1-x^3)^6}{(1-x)^6} \\
\end{align}$$
The numerator and denominator can now be expanded with the binomial theorem, and then long division will simplify the expression. (This is the way I would do it.)
Another approach: 
$$\begin{align}
(x+x^2+x^3)^6 &= (x+(x^2+x^3))^6 \\
&= x^6+6x^5(x^2+x^3) + 15x^4(x^2+x^3)^2 \\
& +\, 20x^3(x^2+x^3)^3 + 15x^2(x^2+x^3)^4 + 6x(x^2+x^3)^5 + (x^2+x^3)^6
\end{align}$$
Now, each of the binomials can be expanded as above.
