a(n) is the sum of the first column of the difference table of the divisors of n.

Terms

a(0) =1a(1) =2a(2) =3a(3) =3a(4) =5a(5) =4a(6) =7a(7) =4a(8) =7a(9) =4a(10) =11a(11) =4a(12) =13a(13) =4a(14) =11a(15) =5a(16) =17a(17) =12a(18) =19a(19) =-3a(20) =13a(21) =4a(22) =23a(23) =-4a(24) =21a(25) =4a(26) =15a(27) =3a(28) =29a(29) =38