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

Terms

a(0) =1a(1) =-1a(2) =6a(3) =-6a(4) =10a(5) =-7a(6) =22a(7) =-26a(8) =26a(9) =-16a(10) =51a(11) =-54a(12) =38a(13) =-41a(14) =101a(15) =-83a(16) =71a(17) =-72a(18) =119a(19) =-143a(20) =123a(21) =-66a(22) =211a(23) =-230a(24) =111a(25) =-151a(26) =279a(27) =-216a(28) =220a(29) =-182