You should have 20 DISTINCT permutations as follows:
{4, 5, 6, 6, 6}, {4, 6, 5, 6, 6}, {4, 6, 6, 5, 6}, {4, 6, 6, 6, 5}, {5, 4, 6, 6, 6}, {5, 6, 4, 6, 6}, {5, 6, 6, 4, 6}, {5, 6, 6, 6, 4}, {6, 4, 5, 6, 6}, {6, 4, 6, 5, 6}, {6, 4, 6, 6, 5}, {6, 5, 4, 6, 6}, {6, 5, 6, 4, 6}, {6, 5, 6, 6, 4}, {6, 6, 4, 5, 6}, {6, 6, 4, 6, 5}, {6, 6, 5, 4, 6}, {6, 6, 5, 6, 4}, {6, 6, 6, 4, 5}, {6, 6, 6, 5, 4} = 20 permutations.