Binary quadratic forms represented by a sum of nonzero squares.

In 1911, Dubouis determined all positive integers that are represented by a sum of k positive squares for any k ≥ 4 . In this article, we generalize Dubouis' result to the binary case. We determine all binary forms that are represented by a sum of k nonzero squares for any k ≥ 5 . [ABSTRACT FROM AUTHOR]