a(n) = Sum_{k=1..n} (-1)^(k+1) * floor(n/(2*k-1))^3.

Terms

a(0) =1a(1) =8a(2) =26a(3) =63a(4) =125a(5) =209a(6) =335a(7) =504a(8) =703a(9) =981a(10) =1311a(11) =1671a(12) =2141a(13) =2681a(14) =3269a(15) =3990a(16) =4808a(17) =5643a(18) =6669a(19) =7847a(20) =8963a(21) =10343a(22) =11861a(23) =13349a(24) =15212a(25) =17170a(26) =19078a(27) =21310a(28) =23748a(29) =26172