a(n) = floor(n/2) + 1 - d(n), where d(n) is the number of divisors of n.

Terms

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