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 A141355 #9 Apr 19 2025 23:48:03 %S A141355 1,1,5,11,43,85,341,683,2731,5461,21845,43691,174763,349525,1398101, %T A141355 2796203,11184811,22369621,89478485,178956971,715827883,1431655765, %U A141355 5726623061,11453246123,45812984491,91625968981,366503875925,733007751851 %N A141355 The Jacobsthal sequence, dropping each third term. %C A141355 A001045 after removal of the subsequence A132805. %F A141355 a(2n+1)-a(2n) = 6*A015565(n). %F A141355 a(4n+1)=2a(4n)-1. a(4n+2)=4a(4n+1)+1. a(4n+3)=2a(4n+2)+1. a(4n+4)=4a(4n+3)-1. %F A141355 a(2n)= A082311(n). a(2n+1) = A082365(n). - R. J. Mathar, Feb 23 2009 %F A141355 a(n)=7*a(n-2)+8*a(n-4). G.f.: (1+x-2*x^2+4*x^3)/((1-8*x^2)*(1+x^2)). - R. J. Mathar, Feb 23 2009 %o A141355 (Python) %o A141355 def A141355(n): return ((1<<(n+1<<1)-(n+1>>1)-1)|1)//3 # _Chai Wah Wu_, Apr 19 2025 %K A141355 nonn,easy %O A141355 0,3 %A A141355 _Paul Curtz_, Aug 03 2008 %E A141355 Edited and extended by _R. J. Mathar_, Feb 23 2009