  We prove that the number of $1$-factorisations of a generalised Petersen
graph of the type $GP(3k,k)$ is equal to the $k$th Jacobsthal number $J(k)$ if
$k$ is odd, and equal to $4J(k)$, when $k$ is even. Moreover, we verify the
list colouring conjecture for $GP(3k,k)$.
