a(n) = sigma_2(3*n).

Terms

a(0) =10a(1) =50a(2) =91a(3) =210a(4) =260a(5) =455a(6) =500a(7) =850a(8) =820a(9) =1300a(10) =1220a(11) =1911a(12) =1700a(13) =2500a(14) =2366a(15) =3410a(16) =2900a(17) =4100a(18) =3620a(19) =5460a(20) =4550a(21) =6100a(22) =5300a(23) =7735a(24) =6510a(25) =8500a(26) =7381a(27) =10500a(28) =8420a(29) =11830