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Search: id:A026646
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| 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; listen)
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OFFSET
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0,2
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COMMENT
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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 (pbarry(AT)wit.ie), Mar 06 2008
Partial sums of A026644, which are the row sums of A026637. - Paul Barry (pbarry(AT)wit.ie), Mar 06 2008
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FORMULA
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G.f.: [1-x^2+2x^3]/[(1-x)(1-2x)(1-x^2)]. - R. 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 (pbarry(AT)wit.ie), Mar 06 2008
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CROSSREFS
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Cf. A000126.
Sequence in context: A089116 A065545 A110930 this_sequence A026668 A111210 A033489
Adjacent sequences: A026643 A026644 A026645 this_sequence A026647 A026648 A026649
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KEYWORD
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nonn
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AUTHOR
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Clark Kimberling (ck6(AT)evansville.edu)
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