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 A177736 #5 Oct 07 2019 14:10:27
%S A177736 1,4,10,22,40,70,112,172,250,358,502,706,970,1312,1768,2386,3184,4228,
%T A177736 5620,7450,9838,13018,17164,22582,29614,38812,50704,66190,86410,
%U A177736 112834,147256,192118,250564,326686,425962,555478,724024,943540,1229290
%N A177736 Partial sums of A006156.
%C A177736 Partial sums of number of ternary squarefree words of length n. Is this always even after a(0) = 1? If so, there are no prime elements, and the subsequence of semiprime elements begins: 358, 502, 706, 2386, 9838, 112834, 192118, 425962. As Weisstein writes in the Mathworld link from A006156: A "square" word consists of two identical adjacent subwords (for example, acbacb). A squarefree word contains no square words as subwords (for example, abcacbabcb). The only squarefree binary words are a, b, ab, ba, aba, and bab (since aa, bb, aaa, aab, abb, baa, bba, and bbb contain square identical adjacent subwords a, b, a, a, b, a, b, and b, respectively). However, there are arbitrarily long ternary squarefree words.
%F A177736 a(n) = Sum_{i=0..n} A006156(i).
%Y A177736 Cf. A006156, A060688.
%K A177736 nonn
%O A177736 0,2
%A A177736 _Jonathan Vos Post_, May 12 2010