We analyze numerically a two-dimensional λφ 4 theory showing that in the limit of a strong coupling λ → ∞ just the homogeneous solutions for time evolution are relevant in agreement with the duality principle in perturbation theory as presented in [M.Frasca, Phys. Rev. A 58, 3439 (1998)], being negligible the contribution of the spatial varying parts of the dynamical equations. A consequence is that the Green function method works for this non-linear problem in the large coupling limit as in a linear theory. A numerical proof is given for this. With these results at hand, we built a strongly coupled quantum field theory for a λφ 4 interacting field computing the first order correction to the generating functional. Mass spectrum of the theory is obtained turning out to be that of a harmonic oscillator with no dependence on the dimensionality of spacetime. The agreement with the Lehmann-Källen representation of the perturbation series is then shown at the first order.A lot of problems in physics have such a difficult equations to solve that the most natural approach is a numerical one. Weak perturbation theory generally proves to be insufficient to extract all the physics. A well-known case is given by quantum chromodynamics that due to the strength of the coupling constant at low energies, makes useless known perturbation techniques demanding the need for numerical solutions.In the seventies and eighties of the last century a significant attempt to build a perturbation theory for a strongly interacting quantum field theory was proposed [1,2,3,4,5,6,7,8]. In this approach it was stipulated that the perturbation to be considered is the free part of the Lagrangian. Notwithstanding this approach is still studied today [9] no fruitful results have been obtained so far due to the strongly singular perturbation series that is obtained in this way. Rather, the rationale behind this method is really smart as one recognize that just interchanging the two parts of the Lagrangian one gets different perturbation series.This duality in perturbation theory is a general mathematical property of differential equations as was shown in Ref. [10,11]. What makes duality interesting is the general property of the leading order that, while in the weak perturbation case is just a free linear theory whose solution is generally known, for the dual series that holds in the limit of a strongly coupling, that is a coupling going to infinity, one can prove a theorem showing that the adiabatic approximation applies. We also pointed out in recent works [12,13] that in field theory and general relativity the dual perturbation series at the leading order produces a rather interesting result: in a strongly coupled field theory the leading order is ruled by a homogeneous equation, that is, the spatial variation of the field in the equations of the theory becomes negligible. In general relativity this gives precious informations on the space-time near a singularity where the above behavior was conjectured in [14,15,16] and numerically shown in [17]...