Slight improvment to the above: [[12, 19, 6, 14, 4, 9], [ 8, 17, 1, 24, 22, 16], [21, 3, 23, 20, 2, 11], [15, 10, 5, 13, 7, 18]] Score = 37

Slight improvment to the above: [[12, 19, 6, 14, 4, 9], [ 8, 17, 1, 24, 22, 16], [21, 3, 23, 20, 2, 11], [15, 10, 5, 13, 7, 18]] Score = 376.6144674353488 Found by increasing number of iterations to 100000 Sim.annealing followed by an exhaustive pair-swap search to find the local minimum would have found this more efficiently. Possibly there are some further refinements left -- I haven't run the exhaustive pair search on the above!