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 A065506 #14 Mar 12 2024 08:48:15 %S A065506 1,2,7,15,39,84,196,419,928,1965,4227,8871,18742,39032,81481,168606, %T A065506 349011,718371,1477783,3028412,6200296,12660171,25823604,52569417, %U A065506 106908199,217086287,440402878,892384788,1806730377,3654428154 %N A065506 Number of (binary) bit strings of length n having an even length block of 0's followed by an odd length block of 1's. %H A065506 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,3,-5,-2). %F A065506 G.f.: x^3/((1-2*x)*(1-3*x^2-x^3)). %F A065506 a(n) = 2^n - A065455(n). %Y A065506 Cf. A065455. %K A065506 nonn,easy %O A065506 3,2 %A A065506 _Len Smiley_, Nov 26 2001