A224671 Number of (n+1) X 4 0..2 matrices with each 2 X 2 subblock idempotent.

41, 76, 108, 170, 257, 398, 617, 967, 1525, 2421, 3862, 6185, 9934, 15990, 25778, 41604, 67199, 108600, 175575, 283929, 459235, 742871, 1201788, 1944315, 3145732, 5089648, 8234952, 13324142, 21558605, 34882226, 56440277, 91321915, 147761569

Offset

1,1

Comments

Column 3 of A224676.

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 4*a(n-1) -5*a(n-2) +a(n-3) +2*a(n-4) -a(n-5) for n>6.

Conjectures from Colin Barker, Feb 17 2018: (Start)

G.f.: x*(41 - 88*x + 9*x^2 + 77*x^3 - 41*x^4 + x^5) / ((1 - x)^3*(1 - x - x^2)).

a(n) = 5 + (2^(-1-n)*((1-sqrt(5))^n*(-19+29*sqrt(5)) + (1+sqrt(5))^n*(19+29*sqrt(5)))) / sqrt(5) + 4*(1+n) + (1+n)*(2+n)/2 for n>1.

(End)

Example

Some solutions for n=3:
..1..1..1..0....1..0..1..0....1..1..1..2....0..0..0..0....1..1..0..0
..0..0..0..0....1..0..1..0....0..0..0..0....0..0..0..0....0..0..0..0
..1..1..1..1....0..0..1..0....0..0..0..1....0..0..0..0....0..0..0..0
..0..0..0..0....0..0..1..0....0..0..0..1....0..0..0..0....0..0..0..1

Crossrefs

Sequence in context: A142038 A213047 A269426 * A044107 A044488 A335482

Adjacent sequences: A224668 A224669 A224670 * A224672 A224673 A224674

Keyword

nonn

Author

R. H. Hardin, Apr 14 2013

Status

approved