Explanation:
the first suspicion we get from the first terms is that the creation algorithm is a multiplication by 3.
-1/3 × 3 = -1
-1 × 3 = -3
-3 × 3 = -9
then the next term would be
-9 × 3 = -27
and the next
-27 × 3 = -81
and the 7th term, that we have already defined, would be
-81 × 3 = -243
we are correct !
so, the missing terms are
-27, -81