A255663 Number of length n+3 0..3 arrays with at most two downsteps in every n consecutive neighbor pairs.

256, 1024, 4048, 14192, 42653, 112196, 265430, 577464, 1174730, 2262312, 4162792, 7370432, 12625472, 21014456, 34103820, 54115508, 84155145, 128505312, 192998760, 285488992, 416438559, 599648684, 853157474, 1200338032, 1671232268

Offset: 1

Author

R. H. Hardin, Mar 01 2015

Keywords

• nonn

Comments

Row 3 of A255660

Examples

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

Links

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

Crossrefs

Cf. A255660

Formula

Empirical: a(n) = (1/39916800)*n^11 + (1/403200)*n^10 + (1/9072)*n^9 + (109/40320)*n^8 + (63421/1209600)*n^7 + (39319/57600)*n^6 + (1888387/362880)*n^5 + (24707/2240)*n^4 + (4099087/453600)*n^3 + (33487/525)*n^2 + (950843/6930)*n + 28 for n>1