434. The well-known expression $\boldsymbol{F}(n)$, where $n$ denotes a variable positive integer, should be prefixed with a + sign when $n$ is even, and with a - sign when $n$ is odd. How can this be expressed concisely algebraically, without adding any verbal explanation to the formula?
434. $(-1)^{n} F(n)$.

Translate the text above into English, keeping the original text's line breaks and format, and output the translation result directly. 

However, since the provided text is already in a form that is commonly used in both English and Chinese (a mathematical expression), it does not require translation. The expression $(-1)^{n} F(n)$ is already in a universally understood format. Therefore, the output remains:

434. $(-1)^{n} F(n)$.