a(n) = Sum_{d|n} d^(3*(n/d - 1)).

Terms

a(0) =1a(1) =2a(2) =2a(3) =10a(4) =2a(5) =93a(6) =2a(7) =578a(8) =731a(9) =4223a(10) =2a(11) =56765a(12) =2a(13) =262489a(14) =547068a(15) =2359810a(16) =2a(17) =31173510a(18) =2a(19) =152949071a(20) =387538140a(21) =1073743157a(22) =2a(23) =20134371189a(24) =244140627a(25) =68719478935a(26) =282430067924a(27) =618515646977a(28) =2a(30) =2