storage (indexes from 1, not zero)   values
1
1 2           1 2,   2 1,   storage[x-1] + storage[1]
1 2 3         123, 213, 321  storage[x-1] + storage[1]
1 2 3 6       1234, 2134, 3214,  4231, 3412, 4132,   storage[x-1] + storage[1] + storage[2]
1 2 3 6 7      12345, 21345, 32145,  42315, 34125, 41325,   storage[x-1] + storage[1]