Random list constraint

I have been using Excel to produce random lists using a column for the set, one for a series of random numbers and one with the formula =INDEX($B$2:$B$21,RANK(A2,A$2:A$21)) where the A column is the random numbers and the B column the set.

I am now looking for a way to enforce the rule (or to obtain the same result as enforcing such rule) to never have the same element repeated in two contiguous cells in the resulting column.

I though of using predetermined blocks of 4 variables (my N is 16) and switching those, but 1) I don't know how to make something correspond to a block of cells and 2) also in that case there should be rules and alternative blocks.

Anyone knows a solution, possibly that doesn't involve VBA and macros since I have no experience there?