a(n) = Sum_{k=1..n-1} sigma(k)*sigma_3(n-k).

Terms

a(0) =0a(1) =1a(2) =12a(3) =59a(4) =200a(5) =526a(6) =1184a(7) =2399a(8) =4368a(9) =7656a(10) =12316a(11) =19586a(12) =29008a(13) =43244a(14) =60272a(15) =85543a(16) =114000a(17) =156163a(18) =200652a(19) =266504a(20) =333968a(21) =432570a(22) =528704a(23) =673706a(24) =806200a(25) =1008644a(26) =1192584a(27) =1467684a(28) =1707328a(29) =2084676