A269463 Number of length-n 0..4 arrays with no repeated value equal to the previous repeated value.

5, 25, 120, 580, 2780, 13300, 63420, 301780, 1433180, 6795700, 32180220, 152216980, 719335580, 3396714100, 16028713020, 75595396180, 356358069980, 1679206088500, 7909957661820, 37249421039380, 175371521796380, 825484323238900

Offset

1,1

Links

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

Formula

Empirical: a(n) = 7*a(n-1) - 4*a(n-2) - 32*a(n-3).

Empirical g.f.: 5*x*(1 - 2*x - 7*x^2) / ((1 - 4*x)*(1 - 3*x - 8*x^2)). - Colin Barker, Jan 22 2019

Example

Some solutions for n=7:
..1. .3. .0. .3. .3. .2. .2. .2. .1. .2. .0. .1. .2. .0. .1. .0
..4. .1. .0. .0. .4. .0. .4. .4. .0. .3. .4. .4. .2. .4. .2. .3
..3. .0. .2. .2. .0. .4. .3. .4. .1. .0. .0. .2. .3. .1. .3. .1
..0. .1. .1. .1. .4. .1. .3. .3. .4. .0. .2. .3. .3. .0. .2. .4
..1. .0. .3. .4. .1. .4. .1. .2. .4. .2. .0. .4. .1. .1. .1. .0
..4. .4. .4. .2. .0. .0. .2. .0. .0. .2. .1. .4. .4. .3. .1. .3
..1. .2. .2. .3. .3. .2. .4. .0. .0. .1. .4. .1. .1. .2. .4. .3

Crossrefs

Column 4 of A269467.

Sequence in context: A269674 A269602 A089927 * A068539 A123871 A268453

Adjacent sequences: A269460 A269461 A269462 * A269464 A269465 A269466

Keyword

nonn

Author

R. H. Hardin, Feb 27 2016

Status

approved