A class of LCD BCH codes of length $n=\frac{q^m+1}{\lambda }$

LCD BCH codes are an important class of cyclic codes which have efficient encoding and decoding algorithms, but their parameters are difficult to determine. The objective of this paper is to study the LCD BCH codes of length $n=\frac{q^m+1}{\lambda }$, where $\lambda \mid (q+1)$ is an integer. Several types of LCD BCH codes with good parameters are presented, and many optimal linear codes are settled. Moreover, we present the first few largest coset leaders modulo $n=q^m+1,\frac{q^m+1}{2},\frac{3^m+1}{4}$, and partially solve two conjectures about BCH codes.