a(n) = Sum_{k=1..n} (-1)^(k+1) * lcm(n,k) / gcd(n,k).

Terms

a(0) =1a(1) =1a(2) =-2a(3) =13a(4) =-9a(5) =28a(6) =-20a(7) =109a(8) =-11a(9) =151a(10) =-54a(11) =256a(12) =-77a(13) =442a(14) =48a(15) =877a(16) =-135a(17) =757a(18) =-170a(19) =1363a(20) =103a(21) =1816a(22) =-252a(23) =2080a(24) =-59a(25) =3043a(26) =-38a(27) =3982a(28) =-405a(29) =2878