A246474 Number of length n+3 0..3 arrays with no pair in any consecutive four terms totalling exactly 3.

60, 132, 292, 644, 1420, 3132, 6908, 15236, 33604, 74116, 163468, 360540, 795196, 1753860, 3868260, 8531716, 18817292, 41502844, 91537404, 201892100, 445287044, 982111492, 2166115084, 4777517212, 10537145916, 23240406916, 51258331044

Offset

1,1

Links

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

Formula

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

Empirical g.f.: 4*x*(15 + 3*x + 7*x^2) / (1 - 2*x - x^3). - Colin Barker, Nov 06 2018

Example

Some solutions for n=6:
..2....3....2....1....0....2....1....0....0....2....1....3....2....0....2....1
..0....3....2....1....2....2....3....0....2....0....1....3....3....0....2....3
..0....2....2....0....0....2....1....0....2....2....1....3....2....0....3....1
..2....2....2....1....0....2....1....0....2....2....0....3....3....1....3....3
..0....2....3....1....0....2....1....0....2....2....0....1....2....1....2....3
..0....2....3....0....0....2....1....0....3....0....0....1....2....1....3....3
..0....2....3....0....0....3....1....2....3....0....1....1....2....3....3....3
..0....0....3....1....0....2....3....0....3....0....0....3....2....1....2....1
..1....0....2....0....0....3....1....2....2....0....1....1....0....3....2....3

Crossrefs

Column 3 of A246479.

Sequence in context: A044247 A044628 A181190 * A334407 A336628 A336443

Adjacent sequences: A246471 A246472 A246473 * A246475 A246476 A246477

Keyword

nonn

Author

R. H. Hardin, Aug 27 2014

Status

approved