a(n) = Sum_{k=1..n} sigma_2( n/gcd(k,n) ).

Terms

a(0) =1a(1) =6a(2) =21a(3) =48a(4) =105a(5) =126a(6) =301a(7) =388a(8) =567a(9) =630a(10) =1221a(11) =1008a(12) =2041a(13) =1806a(14) =2205a(15) =3116a(16) =4641a(17) =3402a(18) =6517a(19) =5040a(20) =6321a(21) =7326a(22) =11661a(23) =8148a(24) =13125a(25) =12246a(26) =15327a(27) =14448a(28) =23577a(29) =13230