Algebraic Geometry
《Algebraic Geometry》 · 第 296 页 · Chapter IV，Remark 1.3.1
If $X$ is a curve of degree $d$ in $\mathbb P^n$, and $D$ is a hyperplane section $X\cap H$, so that $\mathcal L(D)=\mathcal O_X(1)$, then the Hilbert polynomial tells us that $\chi(\mathcal L(D))=d+1-p_a$.