Smallest prime p such that 3^n divides p^2 - 1.

Terms

a(0) =2a(1) =17a(2) =53a(3) =163a(4) =487a(5) =1459a(6) =4373a(7) =13121a(8) =39367a(9) =472391a(10) =1062881a(11) =1062881a(12) =19131877a(13) =19131877a(14) =57395627a(15) =86093443a(16) =258280327a(17) =3874204891a(18) =6973568801a(19) =6973568801a(20) =188286357653a(21) =188286357653a(22) =188286357653