In this paper we study the Pythagoras number P (OK) for the rings of integers in totally real biquadratic fields K. We continue the work of Tinková towards proving the conjecture by Krásenský, Raška and Sgallová that a biquadratic K satisfies P (OK) 6 if and only if it contains neither 2 nor 5, with only finitely many exceptions. We fully solve two out of three remaining classes of fields by proving that all but finitely many K containing 6 or 7 satisfy P (OK) 6. Furthermore, we present ideas and computations which further support the conjecture also for K containing 3. This enables us to refine the conjecture by explicitly listing the exceptional fields.
Daniel Dombek (Wed,) studied this question.
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