Eisenstein series of weight two
= Eisenstein series of weight two
{c}
{title2=$E_2$}
The series
$$
E_2(\tau)=1-24\sum_{n\geq1}\sigma_1(n)q^n
$$
is quasimodular: $E_2(-1/\tau)=\tau^2E_2(\tau)+6\tau/(\pi i)$.
= Eisenstein series of weight two
{c}
{title2=$E_2$}
The series
$$
E_2(\tau)=1-24\sum_{n\geq1}\sigma_1(n)q^n
$$
is quasimodular: $E_2(-1/\tau)=\tau^2E_2(\tau)+6\tau/(\pi i)$.