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A224660 Number of n X n 0..3 matrices with each 2 X 2 subblock idempotent. 0
4, 16, 72, 142, 332, 668, 1356, 2634, 5046, 9480, 17594, 32286, 58730, 106028, 190204, 339322, 602416, 1064888, 1875104, 3290166, 5754586, 10035236, 17452462, 30275242, 52395822 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 3 of A224665.

LINKS

Table of n, a(n) for n=1..25.

FORMULA

Empirical: a(n) = 6*a(n-1) -12*a(n-2) +5*a(n-3) +12*a(n-4) -12*a(n-5) -3*a(n-6) +6*a(n-7) -a(n-9) for n>10.

EXAMPLE

Some solutions for n=3:

..1..0..1....1..0..0....1..0..0....1..1..0....1..1..3....1..0..2....1..1..1

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

..0..0..1....2..0..0....2..1..1....3..1..1....0..1..1....0..0..1....2..1..1

CROSSREFS

Sequence in context: A161797 A124533 A227034 * A330610 A327541 A158784

Adjacent sequences:  A224657 A224658 A224659 * A224661 A224662 A224663

KEYWORD

nonn,more

AUTHOR

R. H. Hardin, Apr 14 2013

STATUS

approved

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Last modified December 6 10:24 EST 2021. Contains 349563 sequences. (Running on oeis4.)