Length of period of continued fraction expansion of square root of 3^n-1.

Terms

a(0) =1a(1) =2a(2) =1a(3) =2a(4) =10a(5) =2a(6) =19a(7) =2a(8) =25a(9) =2a(10) =156a(11) =2a(12) =149a(13) =2a(14) =580a(15) =2a(16) =716a(17) =2a(18) =6461a(19) =2a(20) =2485a(21) =2a(22) =123256a(23) =2a(24) =64a(25) =2a(26) =8638a(27) =2a(28) =722190a(29) =2