Abstract We investigate the functional equation f (f (x+y) ) =f (x+y) +f (x) f (y), \ x, y R. f (f (x + y) ) = f (x + y) + f (x) f (y), x, y ∈ R. Given a real number c 0, c ≠ 0, it was shown in 5 that there is a non-trivial solution f with f (0) =c f (0) = c iff c is transcendental and >-1 > - 1. In that case all values of f are transcendental. In this paper we find all solutions of the functional equation, discuss their odd properties and the connection with ideals in a group algebra.
Johannes Schoißengeier (Thu,) studied this question.
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