a(n) = Sum_{k=1..n} binomial(n,k)*phi(k), where phi is the Euler totient function.

Terms

a(0) =1a(1) =3a(2) =8a(3) =20a(4) =49a(5) =117a(6) =272a(7) =620a(8) =1395a(9) =3107a(10) =6852a(11) =14964a(12) =32395a(13) =69647a(14) =149002a(15) =317712a(16) =675749a(17) =1433769a(18) =3033444a(19) =6396320a(20) =13437913a(21) =28130869a(22) =58708304a(23) =122239396a(24) =254141275a(25) =527946013a(26) =1096312050a(27) =2275897660a(28) =4722500707a(29) =9791471587