a(n) is the number of distinct prime divisors of 2*prime(n)+1.

Terms

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