  We study crossed Andreev reflection (CAR) of electrons or holes in normal
metal-superconductor-normal metal junctions and highlight some very strong
effects of the underlying lattice. In particular, we demonstrate that for sharp
interfaces and under certain, albeit generic, symmetry conditions, the CAR
probability exactly vanishes for an even number of atoms in the superconducting
region. This even-odd effect applies notably to NSN junctions made of graphene
nano-ribbons with armchair edges and for zigzag edges with somewhat more
restrictive conditions. We analyze its robustness towards smoothing of the
boundaries or doping of the sample.
