A characteristic triangle for the Euler totient function (A000010).

Terms

a(0) =1a(1) =-1a(2) =1a(3) =1a(4) =-3a(5) =1a(6) =0a(7) =5a(8) =-7a(9) =1a(10) =-4a(11) =22a(12) =23a(13) =-13a(14) =1a(15) =-64a(16) =20a(17) =172a(18) =29a(19) =-19a(20) =1a(21) =-240a(22) =-1120a(23) =-496a(24) =354a(25) =111a(26) =-29a(27) =1a(28) =2656a(29) =1760