In a algorithm book I'm reading there's this paragraph (it concerns a recursive algorithm for integer multiplication):
In general, a number $x$ with an even number $n$ of digits can be expressed in terms of two $n/2$-digit numbers, its first half $a$ and second half $b$:
$x=10^{n/2} * a + b$
I'm not sure how to apply this formula and what "...its first half $a$ and second half $b$" means exactly.
Suppose $x = 5112$.
This number has $n = 4$ even digits, therefore it should involve a multiplication for $10^{4/2}$; what are $a$ and $b$ in this case?