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 A033489 #12 Jul 08 2025 19:53:08 %S A033489 1,3,7,17,37,81,169,355,727,1491,3019,6119,12319,24807,49783,99921, %T A033489 200197,401121,802969,1607429,3216349,6435717,12874453,25755025, %U A033489 51516169,103044657,206101633,412228073,824480953,1649011689 %N A033489 a(1) = 1, a(n) = 2*a(n-1) + a([n/2]). %p A033489 A033489 := proc(n) option remember; if n = 1 then 1 else A033489(n-1)+A033489(round(2*(n-1)/2))+A033489(round((n-1)/2)); fi; end; %o A033489 (PARI) a(n)=if(n<2,1,(2*a(n-1)+a(floor(n/2)))) %K A033489 nonn %O A033489 1,2 %A A033489 _N. J. A. Sloane_ %E A033489 Better description and more terms from _Benoit Cloitre_, Jan 06 2004