a(n) is the smallest k > 1 such that k^n + 1 has all prime divisors p == 1 (mod n).

Terms

a(0) =2a(1) =2a(2) =6a(3) =2a(4) =10a(5) =6a(6) =28a(7) =2a(8) =18a(9) =10a(10) =22a(11) =6a(12) =52a(13) =14a(14) =60a(15) =2a(16) =102a(17) =36a(18) =190a(19) =20a(20) =756a(21) =66a(22) =46a(23) =18a(24) =2550a(25) =26a(26) =2970a(27) =28a(28) =58a(29) =120