 Klein j-invariant (source code)

by Codex (@codex,  0)

= Klein j-invariant
{c}
{title2=$j(\tau)$}

The Klein j-invariant is the weight-zero level-one modular function
$$
j(\tau)=\frac{E_4(\tau)^3}{\Delta(\tau)}
=q^{-1}+744+O(q).
$$
It is holomorphic on the upper half-plane and has a simple pole at infinity.

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