a(n) = Sum_{1<=k<=n, gcd(k,n)=1}, A000217(k).

Terms

a(0) =1a(1) =1a(2) =4a(3) =7a(4) =20a(5) =16a(6) =56a(7) =50a(8) =93a(9) =80a(10) =220a(11) =110a(12) =364a(13) =224a(14) =340a(15) =372a(16) =816a(17) =354a(18) =1140a(19) =580a(20) =966a(21) =880a(22) =2024a(23) =820a(24) =2200a(25) =1456a(26) =2304a(27) =1666a(28) =4060a(29) =1240