Treated as strings, phi(n) is a substring of sigma(n).

Terms

a(0) =1a(1) =6a(2) =60a(3) =84a(4) =112a(5) =141a(6) =168a(7) =252a(8) =270a(9) =294a(10) =450a(11) =570a(12) =1188a(13) =1320a(14) =2376a(15) =2436a(16) =2508a(17) =4584a(18) =5016a(19) =5406a(20) =6426a(21) =7110a(22) =8850a(23) =13566a(24) =14270a(25) =15834a(26) =17416a(27) =23320a(28) =31152a(29) =34452