Even integers concatenated with themselves.

Terms

a(0) =22a(1) =44a(2) =66a(3) =88a(4) =1010a(5) =1212a(6) =1414a(7) =1616a(8) =1818a(9) =2020a(10) =2222a(11) =2424a(12) =2626a(13) =2828a(14) =3030a(15) =3232a(16) =3434a(17) =3636a(18) =3838a(19) =4040a(20) =4242a(21) =4444a(22) =4646a(23) =4848a(24) =5050a(25) =5252a(26) =5454a(27) =5656a(28) =5858a(29) =6060