Let $D$ in $Z/2[[x]]$ be $\sum x^{ n^{ 2}}$, $n>0$ and prime to $6$. Let $W$ be spanned by the $D^{ k}$, $k>0$ and prime to $6$. Then the formal Hecke operators $T_{ p}$, $p>3$, stabilize $W$, and it can be shown that they act locally nilpotently. We show that the completion of the Hecke algebra generated by these $T_{ p}$ acting on $W$, with respect to the maximal ideal generated by the $T_{ p}$, is a power series ring in $T_{ 7}$ and $T_{ 13}$ with an element of square $0$ adjoined. This may be viewed as a level 3 analog of the level 1 results of Nicolas and Serre -- the Hecke stable space they study is spanned by the odd powers of the mod $2$ reduction of $\Delta$, and their resulting completed Hecke algebra is a power series ring in $T_{ 3}$ and $T_{ 5}$.
Categories: math.NT
