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 A263997 Sequence of block lengths in a block spiral of width 1. 2

%I

%S 1,2,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,

%T 15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,

%U 27,27,28,28,29,29,30,30,31,31,32,32,33

%N Sequence of block lengths in a block spiral of width 1.

%C A left-handed block spiral is created by the following pattern: Start with a 1 X 1 square [ a(1)=1 ]. Attach a block of length 2 and width 1 (a horizontal 1 X 2 rectangle) to the upper side of the square [ a(2)=2 ] pointing to the right. Attach to the corner a vertical 2 X 1 block (rectangle). This block has length 2, so a(3)=2. Continue with a horizontal 1 X 2 block, so a(4) = 2. And so on. See the sketch shown in the link.

%H Hans G. Oberlack, <a href="/A263997/a263997.pdf">Sketch of a block spiral</a>

%F a(n) = a(n-2) + 1 for n > 4.

%F O.g.f.: x*(1+x-x^2-x^3+x^4)/((1-x)*(1-x^2)). From A008619. - _Wolfdieter Lang_, Jan 05 2016

%Y Essentially the same as A008619.

%K nonn,easy

%O 1,2

%A _Hans G. Oberlack_, Oct 31 2015

%E Edited by _Wolfdieter Lang_, Jan 05 2016

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Last modified June 16 06:46 EDT 2019. Contains 324145 sequences. (Running on oeis4.)