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

Terms

a(0) =1a(1) =0a(2) =1a(3) =4a(4) =1a(5) =26a(6) =1a(7) =56a(8) =1a(9) =44a(10) =1a(11) =264a(12) =1a(13) =814a(14) =1a(15) =136a(16) =1a(17) =3730a(18) =1a(19) =20968a(20) =1a(21) =2448a(22) =1a(23) =287980a(24) =1a(25) =397238a(26) =1a(27) =2678a(28) =1a(29) =670896