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

Terms

a(0) =0a(1) =3a(2) =8a(3) =80a(4) =99a(5) =323a(6) =360a(7) =575a(8) =840a(9) =4224a(10) =5775a(11) =9999a(12) =32760a(13) =36480a(14) =36863a(15) =42024a(16) =84680a(17) =349280a(18) =808200a(19) =829920a(20) =848240a(21) =998000a(22) =999999a(23) =3055503a(24) =3272480a(25) =3426200a(26) =3640463a(27) =3644280a(28) =3682560a(29) =5597955