a(n) = Sum_{k<=n} A000203(k)*(n-k+1), where A000203(m) is the sum of divisors of m.

Terms

a(0) =1a(1) =5a(2) =13a(3) =28a(4) =49a(5) =82a(6) =123a(7) =179a(8) =248a(9) =335a(10) =434a(11) =561a(12) =702a(13) =867a(14) =1056a(15) =1276a(16) =1514a(17) =1791a(18) =2088a(19) =2427a(20) =2798a(21) =3205a(22) =3636a(23) =4127a(24) =4649a(25) =5213a(26) =5817a(27) =6477a(28) =7167a(29) =7929