These builds typically include refinements to the Linux kernel.
What is this file for? (e.g., a Retroid Pocket, a tablet, or a specific control board?) Are you writing this for a technical class or a blog post ?
At its core, a 3.1-series build often signifies a move toward stability following a major version leap. The alphanumeric string "a13e63cd" serves as a unique commit hash, identifying the exact state of the source code at the time of compilation.