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A224669 Number of (n+1) X 2 0..2 matrices with each 2 X 2 subblock idempotent. 1

%I

%S 12,25,41,70,115,189,308,501,813,1318,2135,3457,5596,9057,14657,23718,

%T 38379,62101,100484,162589,263077,425670,688751,1114425,1803180,

%U 2917609,4720793,7638406,12359203,19997613,32356820,52354437,84711261,137065702

%N Number of (n+1) X 2 0..2 matrices with each 2 X 2 subblock idempotent.

%C Column 1 of A224676.

%H R. H. Hardin, <a href="/A224669/b224669.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 2*a(n-1) -a(n-3).

%F Conjectures from _Colin Barker_, Feb 17 2018: (Start)

%F G.f.: x*(12 + x - 9*x^2) / ((1 - x)*(1 - x - x^2)).

%F a(n) = -4 + (2^(-1-n)*((1-sqrt(5))^n*(-19+13*sqrt(5)) + (1+sqrt(5))^n*(19+13*sqrt(5)))) / sqrt(5).

%F (End)

%e Some solutions for n=3:

%e ..1..0....0..0....0..0....1..0....1..2....1..2....0..0....1..2....1..1....0..0

%e ..1..0....0..0....1..1....0..1....0..0....0..0....0..1....0..0....0..0....1..1

%e ..0..1....0..0....0..0....0..1....0..0....0..0....0..1....0..0....1..1....0..0

%e ..0..1....2..1....0..0....0..1....1..1....0..0....0..1....2..1....0..0....0..1

%K nonn

%O 1,1

%A _R. H. Hardin_, Apr 14 2013

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Last modified October 17 17:21 EDT 2021. Contains 348065 sequences. (Running on oeis4.)