A239812 Number of n X 1 0..3 arrays with no element equal to zero plus the sum of elements to its left or one plus the sum of elements above it, modulo 4.

2, 5, 11, 25, 57, 129, 293, 665, 1509, 3425, 7773, 17641, 40037, 90865, 206221, 468025, 1062197, 2410689, 5471133, 12416905, 28180549, 63956625, 145151533, 329425881, 747642197, 1696797025, 3850933181, 8739811625, 19835272037, 45016761649

Offset: 1

Author

R. H. Hardin, Mar 27 2014

Keywords

• nonn

Comments

Column 1 of A239819.

Examples

			Some solutions for n=5:
..2....2....2....2....3....2....2....3....2....3....2....2....3....3....2....3
..1....1....2....2....1....1....1....3....2....1....1....1....2....3....2....2
..3....2....3....2....2....3....2....2....2....3....2....3....1....1....2....3
..1....1....2....1....1....1....3....3....1....3....1....1....1....3....2....2
..1....2....1....2....1....3....3....3....3....1....1....2....2....1....3....2
		

Links

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

Crossrefs

Cf. A239819.

Formula

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

Empirical g.f.: x*(2 + 3*x + 2*x^2) / (1 - x - 2*x^2 - 2*x^3). - Colin Barker, Feb 21 2018