Both n and its reverse are one less than a square.

Terms

a(0) =0a(1) =3a(2) =8a(3) =99a(4) =323a(5) =575a(6) =4224a(7) =5775a(8) =9999a(9) =36863a(10) =42024a(11) =999999a(12) =3055503a(13) =3640463a(14) =5597955a(15) =8803088a(16) =32855823a(17) =99999999a(18) =360696063a(19) =422919224a(20) =4227990528a(21) =8250997224a(22) =9999999999a(23) =30485858403a(24) =30536863503a(25) =32154945123