  Pairing of electrons is ubiquitous in electronic systems featuring attractive
inter-electron interactions, as exemplified in superconductors.
Counter-intuitively, it can also be mediated in certain circumstances by the
repulsive Coulomb interaction alone. Quantum Hall (QH) Fabry-P\'erot
interferometers (FPIs) tailored in two-dimensional electron gas under a
perpendicular magnetic field has been argued to exhibit such unusual electron
pairing seemingly without attractive interaction. Here, we show evidence in
graphene QH FPIs revealing not only a similar electron pairing at bulk filling
factor nu=2 but also an unforeseen emergence of electron tripling characterized
by a fractional Aharonov-Bohm flux period h/3e (h is the Planck constant and e
the electron charge) at nu=3. Leveraging a novel plunger-gate spectroscopy, we
demonstrate that electron pairing (tripling) involves correlated charge
transport on two (three) entangled QH edge channels. This spectroscopy
indicates a quantum interference flux-periodicity determined by the sum of the
phases acquired by the distinct QH edge channels having slightly different
interfering areas. While recent theory invokes the dynamical exchange of
neutral magnetoplasmons -- dubbed neutralons -- as mediator for electron
pairing, our discovery of three entangled QH edge channels with apparent
electron tripling defies understanding and introduces a new three-body problem
for interacting fermions.
