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

Terms

a(0) =2a(1) =2a(2) =2a(3) =4a(4) =2a(5) =6a(6) =6a(7) =6a(8) =2a(9) =24a(10) =12a(11) =6a(12) =6a(13) =6a(14) =30a(15) =60a(16) =2a(17) =6a(18) =210a(19) =6a(20) =6a(21) =60a(22) =30a(23) =6a(24) =30a(25) =210a(26) =210a(27) =240a(28) =6a(29) =30