a(n) = Sum_{k=1..n-1} sigma(k) * sigma_2(n-k).

Terms

a(0) =0a(1) =1a(2) =8a(3) =29a(4) =78a(5) =170a(6) =324a(7) =579a(8) =918a(9) =1472a(10) =2106a(11) =3126a(12) =4174a(13) =5904a(14) =7500a(15) =10189a(16) =12458a(17) =16563a(18) =19574a(19) =25312a(20) =29538a(21) =37320a(22) =42456a(23) =53472a(24) =59456a(25) =73482a(26) =81806a(27) =99268a(28) =108352a(29) =132084