For what values of a in R (real numbers) is the function (1+x^2)^a in L^2
NOTE: let L^2 be like in Lebesgue integration where the set of all measurable functions that are square-integrable forms a Hilbert space, the so-called L2 space.
Keywords: integration, integrates, integrals, integrating, double, triple, multiple, riemann integrable, lebesgue integrable