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 A104723 #6 Feb 06 2020 14:50:05
%S A104723 0,1,0,2,4,10,18,42,80,168,330,682,1340,2730,5418,10910,21760,43690,
%T A104723 87192,174762,349180,699006,1397418,2796202,5590960,11184800,22366890,
%U A104723 44739072,89473020,178956970,357902670,715827882,1431633920,2863310846
%N A104723 Moebius transform of Jacobsthal numbers.
%F A104723 a(n) = Sum_{d|n} mu(n/d)*A001045(d).
%F A104723 a(n+3) = 3*A027375(n+3) (since the Moebius transform of (-1)^n is (-1, -1, 2, 0, 0, 0, ...)).
%F A104723 G.f.: Sum_{k>=1} mu(k) * x^k / (1 - x^k - 2*x^(2*k)). - _Ilya Gutkovskiy_, Feb 06 2020
%Y A104723 Cf. A001045, A309729.
%K A104723 nonn
%O A104723 0,4
%A A104723 _Paul Barry_, Mar 20 2005