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 A306742 #13 Mar 24 2019 06:42:28 %S A306742 0,4,6,14,26,54,104,210,412,832,1654,3330,6670,13452,27004,54414, %T A306742 109400,220264,442938,891256,1791894,3603128,7241452,14552628, %U A306742 29234478,58720290,117911510,236729446,475169660,953616548,1913446072,3838773120,7700145556,15443494464,30969376788,62096345834,124493833506 %N A306742 Number of length-n binary words that can be written as the concatenation of two unbordered binary words. %C A306742 A word w is bordered if it has a nonempty prefix, unequal to w, that is also a suffix. A word is unbordered if it is not bordered. %e A306742 For n = 5, the 6 words that are not so expressible are 00000, 00100, 01010, and their complements. %Y A306742 Cf. A003000. %K A306742 nonn %O A306742 1,2 %A A306742 _Jeffrey Shallit_, Mar 07 2019 %E A306742 a(23)-a(37) from _Bert Dobbelaere_, Mar 24 2019