function mathematics (ary = [ ], n = ary.length) { if (1 === n) { return ary.map (a=> [a]); } else { return ary.flatMap ((a, i)=> mathematics (ary.slice (i), n -1).map (b=> [a,...b])) } } console.log (mathematics ([1,2,3],3)); /* [1,1,1], …