Concatenate (1,n,n,1).

Terms

a(0) =1001a(1) =1111a(2) =1221a(3) =1331a(4) =1441a(5) =1551a(6) =1661a(7) =1771a(8) =1881a(9) =1991a(10) =110101a(11) =111111a(12) =112121a(13) =113131a(14) =114141a(15) =115151a(16) =116161a(17) =117171a(18) =118181a(19) =119191a(20) =120201a(21) =121211a(22) =122221a(23) =123231a(24) =124241a(25) =125251a(26) =126261a(27) =127271a(28) =128281a(29) =129291