Improved upper bound on A(18,8)

Abstract

For nonnegative integers $n$ and $d$, let $A(n,d)$ be the maximum cardinality of a binary code of length $n$ and minimum distance at least $d$. We consider a slight sharpening of the semidefinite programming bound of Gijswijt, Mittelmann and Schrijver, and obtain that $A(18,8)\leq 70$.