5. (1992 Shanghai Municipal Competition) $f(x)$ is a function defined on the set of non-negative integers, for any positive integer $x$, we have $f(x)=f(x-1)+f(x+1)$, and $f(0)=1992$. Then $f(1992)=$ $\qquad$ .
5. Fill in 1992. Reason: From $f(x)=f(x-1)+f(x+1)$

we have $f(x+1)=f(x)+f(x+2)$
$$
f(x-2)=f(x+1)+f(x+3)
$$

From (1), (2), and (3) combined, we solve to get $f(x)=-f(x+3)$, thus $f(x+6)=f[(x+3)+3]=-f(x+3)=$ $-[-f(x)]=f(x)$, which means $f(x)$ is a periodic function with 6 as its period (this can also be directly derived from Conclusion 6(3) in Chapter 1), hence $f(1992)=f(332 \cdot 6+0)=f(0)=1992$.