a(n) is the number of unitary divisors of n (d such that d divides n, gcd(d, n/d) = 1).

Terms

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