Sums of squares in Quaternion rings
  Lagrange's Four Squares Theorem states that any positive integer can be expressed as the sum of four integer squares. We investigate the analogous question over Quaternion rings, focusing on squares of elements of Quaternion rings with integer coefficients. We determine the minimum necessary number of squares for infinitely many Quaternion rings, and give global upper and lower bounds. 
Anna Cooke, Spencer Hamblen, and Sam Whitfield
math.NT