Sum of proper divisors (or aliquot parts) of n: sum of divisors of n that are less than n.

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =1a(5) =6a(6) =1a(7) =7a(8) =4a(9) =8a(10) =1a(11) =16a(12) =1a(13) =10a(14) =9a(15) =15a(16) =1a(17) =21a(18) =1a(19) =22a(20) =11a(21) =14a(22) =1a(23) =36a(24) =6a(25) =16a(26) =13a(27) =28a(28) =1a(29) =42