Product Symbol for sequences in decrementing order

Question

What is the symbol for a product of elements in some range $\displaystyle \prod_{i=4}^{1} i = 4 \times 3 \times 2 \times 1$ in reversed order? I thought of $\displaystyle\coprod_{i=1}^{4} i$ but it stands for coproduct :-)

Answer 1

You can just index it in a decreasing fashion:

$$ \Pi_{i=1}^4 (4-i+1)$$

Answer 2

$$\prod_{i=1}^{4}(5-i)=4\times 3\times 2\times 1$$

I don't think there is a special symbol for it. If you have a product $$\prod_{i=1}^{n}f(i)=f(1)\times f(2)\times\ldots\times f(n)$$ and want to reverse it you can replace $i$ with $n+1-i$ such that $$\prod_{i=1}^{n}f(n+1-i)=f(n)\times f(n-1)\times\ldots\times f(1)$$