Self-composition of the Euler totient function (A000010).

Terms

a(0) =1a(1) =2a(2) =6a(3) =15a(4) =42a(5) =106a(6) =280a(7) =702a(8) =1778a(9) =4398a(10) =10910a(11) =26678a(12) =65172a(13) =157656a(14) =380524a(15) =912846a(16) =2185906a(17) =5216588a(18) =12433166a(19) =29564544a(20) =70189672a(21) =166245574a(22) =392909240a(23) =926290066a(24) =2178881218a(25) =5114469170a(26) =11985221654a(27) =28049398284a(28) =65588182636a(29) =153277006212