Abstract
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 $T_{5}$.