  We study the Einstein-Maxwell system of equations in spherically symmetric
gravitational fields for static interior spacetimes. The condition for pressure
isotropy is reduced to a recurrence equation with variable, rational
coefficients. We demonstrate that this difference equation can be solved in
general using mathematical induction. Consequently we can find an explicit
exact solution to the Einstein-Maxwell field equations. The metric functions,
energy density, pressure and the electric field intensity can be found
explicitly. Our result contains models found previously including the neutron
star model of Durgapal and Bannerji. By placing restrictions on parameters
arising in the general series we show that the series terminate and there exist
two linearly independent solutions. Consequently it is possible to find exact
solutions in terms of elementary functions, namely polynomials and algebraic
functions.
