a(n) = Sum_{k=1..n} (-1)^(k+1) * floor(n/k)^5.

Terms

a(0) =1a(1) =31a(2) =243a(3) =992a(4) =3094a(5) =7564a(6) =16596a(7) =31744a(8) =58237a(9) =97117a(10) =158169a(11) =241837a(12) =364299a(13) =521829a(14) =745693a(15) =1018120a(16) =1389402a(17) =1837302a(18) =2423834a(19) =3105432a(20) =3998776a(21) =5007286a(22) =6289998a(23) =7738784a(24) =9543887a(25) =11537207a(26) =14031231a(27) =16717879a(28) =20018661a(29) =23629281