a(n) is the least prime factor (> 3) in the factorization of 2^(2*prime(n))-1.

Terms

a(0) =5a(1) =7a(2) =11a(3) =43a(4) =23a(5) =2731a(6) =43691a(7) =174763a(8) =47a(9) =59a(10) =715827883a(11) =223a(12) =83a(13) =431a(14) =283a(15) =107a(16) =2833a(18) =7327657a(19) =228479a(20) =439a(21) =2687a(22) =167a(23) =179a(24) =971a(26) =2550183799a(27) =643a(28) =104124649a(29) =227a(31) =263a(32) =1097