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 A026646 a(n) = Sum_{0<=i,j<=n} A026637(i,j). 1
 1, 3, 7, 17, 37, 79, 163, 333, 673, 1355, 2719, 5449, 10909, 21831, 43675, 87365, 174745, 349507, 699031, 1398081, 2796181, 5592383, 11184787, 22369597, 44739217, 89478459, 178956943, 357913913, 715827853, 1431655735 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS 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 Partial sums of A026644, which are the row sums of A026637. - Paul Barry, Mar 06 2008 LINKS FORMULA G.f.: [1-x^2+2x^3]/[(1-x)(1-2x)(1-x^2)]. - Ralf Stephan, Apr 30 2004 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 a(n+1) = 2*a(n) + A109613(n), a(0)=1. - Paul Curtz, Sep 22 2019 MATHEMATICA CoefficientList[Series[(1-x^2+2x^3)/((1-x)(1-2x)(1-x^2)), {x, 0, 29}], x] (* Metin Sariyar, Sep 22 2019 *) CROSSREFS Cf. A000126. Cf. A026637, A026644, A109613. Sequence in context: A244629 A065545 A110930 * A026668 A111210 A033489 Adjacent sequences:  A026643 A026644 A026645 * A026647 A026648 A026649 KEYWORD nonn AUTHOR STATUS approved

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Last modified July 4 12:21 EDT 2022. Contains 355075 sequences. (Running on oeis4.)