A200839 Number of 0..n arrays x(0..3) of 4 elements without any two consecutive increases or two consecutive decreases.

16, 69, 194, 435, 846, 1491, 2444, 3789, 5620, 8041, 11166, 15119, 20034, 26055, 33336, 42041, 52344, 64429, 78490, 94731, 113366, 134619, 158724, 185925, 216476, 250641, 288694, 330919, 377610, 429071, 485616, 547569, 615264, 689045, 769266

Offset: 1

Author

R. H. Hardin Nov 23 2011

Keywords

• nonn

Comments

Row 2 of A200838.

Examples

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

Links

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

Formula

Empirical: a(n) = (5/12)*n^4 + (19/6)*n^3 + (79/12)*n^2 + (29/6)*n + 1.

Conjectures from Colin Barker, Oct 14 2017: (Start)

G.f.: x*(16 - 11*x + 9*x^2 - 5*x^3 + x^4) / (1 - x)^5.

a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5.

(End)