[rand.eng.philox] Change "n-length sequence" to "length-n sequence".

Author: tkoeppe

source/numerics.tex

@@ -3112,13 +3112,10 @@
 \end{codeblock}
 
 \pnum
-The \tcode{Philox} function maps the $n/2$-length sequence $K$ and
-the $n$-length sequence $X$ into
-an $n$-length output sequence $Y$.
-Philox applies an $r$-round substitution-permutation network to
-the values in $X$.
+The \tcode{Philox} function maps the length-$n/2$ sequence $K$ and
+the length-$n$ sequence $X$ into a length-$n$ output sequence $Y$.
+Philox applies an $r$-round substitution-permutation network to the values in $X$.
 A single round of the generation algorithm performs the following steps:
-
 \begin{itemize}
 \item
 The output sequence $X'$ of the previous round