  The effective action and the mean fermion number density of graphene in
constant external magnetic field at finite temperature and density are
calculated. Closed expressions for these are given and their variation with
temperature are studied. It is found that the mean fermion number density peaks
around a particular temperature, depending on the chemical potential at low
temperatures. This feature is interpreted as 'condensation of fermions
${\bar{\psi}}{\psi}$' in graphene. In future, it is interesting to extend and
explore this calculation and the work of the reference [20] for the case of
Graphyne [23].
