Least number with the prime signature of 2^n - 1.

Terms

a(0) =1a(1) =2a(2) =2a(3) =6a(4) =2a(5) =12a(6) =2a(7) =30a(8) =6a(9) =30a(10) =6a(11) =420a(12) =2a(13) =30a(14) =30a(15) =210a(16) =2a(17) =840a(18) =2a(19) =4620a(20) =60a(21) =210a(22) =6a(23) =60060a(24) =30a(25) =30a(26) =30a(27) =30030a(28) =30a(29) =60060