a(n) = Sum_{1 <= i <= j <= k <= n} gcd(i,j,k).

Terms

a(0) =1a(1) =5a(2) =13a(3) =28a(4) =47a(5) =82a(6) =116a(7) =172a(8) =235a(9) =321a(10) =397a(11) =538a(12) =641a(13) =798a(14) =980a(15) =1192a(16) =1361a(17) =1655a(18) =1863a(19) =2218a(20) =2553a(21) =2912a(22) =3210a(23) =3766a(24) =4171a(25) =4661a(26) =5183a(27) =5840a(28) =6303a(29) =7168