My teacher wrote the following about the legendre function without proof
1) $P^{-m}_{n}(x)=(-1)^{m}\frac{(n-m)!}{(n+m)!}P_{n}^{m}(x)$
2) $P_{2n}(0)=\frac{(-1)^{m}}{\sqrt{\pi}}\frac{\Gamma(n+\frac{1}{2})}{\Gamma(n+1)}$
I search for proof online but couldn't find any. Does anyone know how to proof these properties?