a(0) = 0; for n > 0, a(n) = number of proper divisors of n (divisors of n which are less than n).

Terms

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