login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A224669 Number of (n+1) X 2 0..2 matrices with each 2 X 2 subblock idempotent. 1
12, 25, 41, 70, 115, 189, 308, 501, 813, 1318, 2135, 3457, 5596, 9057, 14657, 23718, 38379, 62101, 100484, 162589, 263077, 425670, 688751, 1114425, 1803180, 2917609, 4720793, 7638406, 12359203, 19997613, 32356820, 52354437, 84711261, 137065702 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 1 of A224676.

LINKS

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

FORMULA

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

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

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

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

(End)

EXAMPLE

Some solutions for n=3:

..1..0....0..0....0..0....1..0....1..2....1..2....0..0....1..2....1..1....0..0

..1..0....0..0....1..1....0..1....0..0....0..0....0..1....0..0....0..0....1..1

..0..1....0..0....0..0....0..1....0..0....0..0....0..1....0..0....1..1....0..0

..0..1....2..1....0..0....0..1....1..1....0..0....0..1....2..1....0..0....0..1

CROSSREFS

Sequence in context: A041280 A132754 A250666 * A164577 A195143 A280321

Adjacent sequences:  A224666 A224667 A224668 * A224670 A224671 A224672

KEYWORD

nonn

AUTHOR

R. H. Hardin, Apr 14 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 21 10:46 EDT 2021. Contains 347597 sequences. (Running on oeis4.)