Ryan chooses five subsets S1,S2,S3,S4,S5 of {1,2,3,4,5,6,7} such that ∣S1∣=1, ∣S2∣=2, ∣S3∣=3, ∣S4∣=4, and ∣S5∣=5. Moreover, for all 1≤i<j≤5, either Si∩Sj=Si or Si∩Sj=∅ (in other words, the intersection of Si and Sj is either Si or the empty set). In how many ways can Ryan select the sets?