Résumé
Let$\mathcal{W}_N$be a quantized Borel subalgebra of$U_q(sl(2,\mc))$ , specialized at a primitive root of unity$\omega = \exp(2i\pi/N)$of odd order$N >1$ . One shows that the$6j$ -symbols of cyclic representations of$\mathcal{W}_N$are representations of the canonical element of a certain extension of the Heisenberg double of$\mathcal{W}_N$ . This canonical element is a twisted$q$ -dilogarithm. In particular, one gives explicit formulas for these$6j$ -symbols, and one constructs partial symmetrizations of them, the c- $6j$ -symboles. The latters are at the basis of the construction of the quantum hyperbolic invariants of 3-manifolds.