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

Terms

a(0) =1a(1) =4a(2) =13a(3) =25a(4) =55a(5) =73a(6) =136a(7) =184a(8) =265a(9) =325a(10) =490a(11) =562a(12) =796a(13) =922a(14) =1102a(15) =1294a(16) =1702a(17) =1864a(18) =2377a(19) =2617a(20) =2995a(21) =3325a(22) =4084a(23) =4372a(24) =5122a(25) =5590a(26) =6319a(27) =6823a(28) =8041a(29) =8401