A224019 Number of n X 3 0..3 arrays with rows nondecreasing and antidiagonals unimodal.

20, 400, 6796, 112436, 1859020, 30756756, 508916456, 8420768936, 139333478144, 2305467501680, 38147189410288, 631198698504112, 10444066884547776, 172811720487440320, 2859412053301829248, 47312978931444876928

Offset: 1

Author

R. H. Hardin, Mar 30 2013

Keywords

• nonn

Comments

Column 3 of A224024.

Examples

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

Links

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

Crossrefs

Cf. A224024.

Formula

Empirical: a(n) = 20*a(n-1) - 70*a(n-2) + 228*a(n-3) - 276*a(n-4) + 392*a(n-5) - 196*a(n-6) + 144*a(n-7).

Empirical g.f.: 4*x*(5 + 49*x^2 - 11*x^3 + 85*x^4 - 13*x^5 + 36*x^6) / (1 - 20*x + 70*x^2 - 228*x^3 + 276*x^4 - 392*x^5 + 196*x^6 - 144*x^7). - Colin Barker, Aug 26 2018