This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A077631 #14 Sep 19 2021 08:04:38
%S A077631 2,5,10,17,56,53,160,161,346,485,1850,1457,3764,4373,13468,13121,
%T A077631 43572,39365,192642,118097,226348,354293,2646006,1062881,1871694,
%U A077631 3188645,5646564,9565937,36393508,28697813,143274092,86093441,195407590,258280325,542628818,774840977
%N A077631 Sum of terms in periodic part of continued fraction expansion of square root of -1 + 3^n.
%H A077631 Chai Wah Wu, <a href="/A077631/b077631.txt">Table of n, a(n) for n = 1..52</a>
%F A077631 From _Benoit Cloitre_, Nov 28 2002: (Start)
%F A077631 a(2n) = 2*3^n-1.
%F A077631 Conjecture: if n>1 sqrt(3^(2n+1)) < a(2n+1) < sqrt((2n+1)*3^(2n+1)). (End)
%t A077631 Table[Apply[Plus, Last[ContinuedFraction[Sqrt[ -1+3^u]]]], {u, 1, 25}]
%Y A077631 Cf. A077624-A077635.
%K A077631 nonn
%O A077631 1,1
%A A077631 _Labos Elemer_, Nov 13 2002
%E A077631 a(26)-a(36) from _Chai Wah Wu_, Sep 18 2021