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%I #17 Sep 22 2019 07:56:29
%S 1,3,7,17,37,79,163,333,673,1355,2719,5449,10909,21831,43675,87365,
%T 174745,349507,699031,1398081,2796181,5592383,11184787,22369597,
%U 44739217,89478459,178956943,357913913,715827853,1431655735
%N a(n) = Sum_{0<=i,j<=n} A026637(i,j).
%C a(n) indexes the corner blocks on the Jacobsthal spiral built from blocks of unit area (using J(1) and J(2) as the sides of the first block). - _Paul Barry_, Mar 06 2008
%C Partial sums of A026644, which are the row sums of A026637. - _Paul Barry_, Mar 06 2008
%F G.f.: [1-x^2+2x^3]/[(1-x)(1-2x)(1-x^2)]. - _Ralf Stephan_, Apr 30 2004
%F a(n)=J(n+3)-2*floor((n+2)/2), where J(n)=A001045(n) the Jacobsthal numbers; a(n)=1+sum{k=0..n, J(k+2)-1}; - _Paul Barry_, Mar 06 2008
%F a(n+1) = 2*a(n) + A109613(n), a(0)=1. - _Paul Curtz_, Sep 22 2019
%t CoefficientList[Series[(1-x^2+2x^3)/((1-x)(1-2x)(1-x^2)), {x, 0, 29}], x] (* _Metin Sariyar_, Sep 22 2019 *)
%Y Cf. A000126.
%Y Cf. A026637, A026644, A109613.
%K nonn
%O 0,2
%A _Clark Kimberling_
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