a(n) = smallest prime > lcm(1..n).

Terms

a(0) =2a(1) =2a(2) =3a(3) =7a(4) =13a(5) =61a(6) =61a(7) =421a(8) =853a(9) =2521a(10) =2521a(11) =27733a(12) =27733a(13) =360391a(14) =360391a(15) =360391a(16) =720743a(17) =12252259a(18) =12252259a(19) =232792561a(20) =232792561a(21) =232792561a(22) =232792561a(23) =5354228921a(24) =5354228921a(25) =26771144401a(26) =26771144401a(27) =80313433231a(28) =80313433231