a(n) = phi(prime(n)+1).

Terms

a(0) =2a(1) =2a(2) =2a(3) =4a(4) =4a(5) =6a(6) =6a(7) =8a(8) =8a(9) =8a(10) =16a(11) =18a(12) =12a(13) =20a(14) =16a(15) =18a(16) =16a(17) =30a(18) =32a(19) =24a(20) =36a(21) =32a(22) =24a(23) =24a(24) =42a(25) =32a(26) =48a(27) =36a(28) =40a(29) =36