a(n) is the least prime such that the multiplicative order of 5 mod a(n) equals n.

Terms

a(0) =2a(1) =3a(2) =31a(3) =13a(4) =11a(5) =7a(6) =19531a(7) =313a(8) =19a(9) =521a(10) =12207031a(11) =601a(12) =305175781a(13) =29a(14) =181a(15) =17a(16) =409a(17) =5167a(18) =191a(19) =41a(20) =379a(21) =23a(22) =8971a(23) =390001a(24) =101a(25) =5227a(26) =109a(27) =234750601a(28) =59a(29) =61