I am working on the spherical harmonic decomposition of cosmic microwave background maps, therefore I often deal with functions that are proportional to Wigner 3J symbols/Clebsch–Gordan coefficients. I would be very grateful if you could share with me a closed form of the ratio between $$ \begin{pmatrix} l_1 &l_2 &l_3\\ 0&2&-2 \end{pmatrix} $$ and $$ \begin{pmatrix} l_1 &l_2 &l_3\\ 0&0&0 \end{pmatrix} \;, $$ for $l_1+l_2+l_3$ even, if it exists. Ideally, I would like an expansion of the first 3j-symbol in terms of the second one, i.e. first_3j = second_3j * ( 1 + ... ) Thank you for your consideration. Best wishes, Guido