N r = | { x ∣ R x = r } | {\displaystyle N_{r}=|\{x\mid R_{x}=r\}|} For example, N 1 {\displaystyle N_{1}} is the number of species for which only one individual was observed.
N r = | { x ∣ R x = r } | {\displaystyle N_{r}=|\{x\mid R_{x}=r\}|} 例えば  N 1 {\displaystyle N_{1}}  は1つしか個体が観測されなかった種の数を表す。