“…It is not hard to see that there are only 14 of them (see also [14, Table 1]) with a = (1, 1, 1, 1), (1, 1, 1, 3), (1, 1, 2, 2), (1, 1, 2, 4), (1,1,4,6), (1,2,2,5), (1,2,3,6), (1,2,6,9), (1,3,4,4), (1,3,8,12), (1,4,5,10), (1,6,14,21), (2,3,3,4), (2,3,10,15).…”