Another.

Sympy and networkx, man; I'm tellin' ya

Author: offby1

66.py

@@ -0,0 +1,17 @@
+import operator
+
+from sympy.solvers.diophantine.diophantine import diop_DN
+
+
+def min_x(x_y_tuples):
+    return min(x_y_tuples, key=operator.itemgetter(0))
+
+
+def solution_for(D):
+    solutions = diop_DN(D, 1)
+    return min_x(solutions)
+
+
+solutions = [(solution_for(D), D) for D in range(2, 1001)]
+print(max(solutions, key=operator.itemgetter(0)))
+# ((16421658242965910275055840472270471049, 638728478116949861246791167518480580), 661)