Palindromes of the form b^k + 1 or b^k - 1, with b, k > 1.

Terms

a(0) =3a(1) =5a(2) =7a(3) =8a(4) =9a(5) =33a(6) =99a(7) =101a(8) =242a(9) =323a(10) =575a(11) =626a(12) =999a(13) =1001a(14) =4224a(15) =5775a(16) =7777a(17) =9999a(18) =10001a(19) =29792a(20) =36863a(21) =42024a(22) =99999a(23) =100001a(24) =999999a(25) =1000001a(26) =1040401a(27) =2217122a(28) =3055503a(29) =3640463