a(n) = Sum_{k=1..n} (-1)^(k-1) * binomial(k+3,4) * floor(n/k).

Terms

a(0) =1a(1) =-3a(2) =13a(3) =-26a(4) =45a(5) =-70a(6) =141a(7) =-228a(8) =283a(9) =-366a(10) =636a(11) =-879a(12) =942a(13) =-1232a(14) =1914a(15) =-2331a(16) =2515a(17) =-3090a(18) =4226a(19) =-5313a(20) =5539a(21) =-6114a(22) =8837a(23) =-10558a(24) =9988a(25) =-11947a(26) =15969a(27) =-17705a(28) =18256a(29) =-20364