An Exceptional Splitting of Khovanov's Arc Algebras in Characteristic 2

We show that there is an associative algebra ${\tilde{H}}_n$ such that, over a base ring $R$ of characteristic 2, Khovanov’s arc algebra $H_n$ is isomorphic to the algebra ${\tilde{H}}_n[x]\mathrm{/}(x^2)$. We also show a similar result for bimodules associated to planar tangles and prove that there is no such isomorphism over $\mathbb{Z}$.