A250346 Number of length n arrays x(i), i=1..n with x(i) in i..i+3 and no value appearing more than 2 times.

4, 16, 62, 235, 888, 3349, 12620, 47545, 179104, 674666, 2541362, 9572864, 36059224, 135828387, 511640114, 1927252354, 7259597884, 27345542237, 103005522894, 388002462425, 1461532415920, 5505318159061, 20737499694808, 78114267177504

Offset: 1

Author

R. H. Hardin, Nov 19 2014

Keywords

• nonn

Examples

			Some solutions for n=6:
..3....1....1....1....3....1....1....0....3....2....1....2....0....1....0....0
..2....2....3....4....2....1....4....4....4....2....3....4....2....2....3....1
..5....4....2....2....3....4....2....3....2....4....3....5....2....2....4....2
..4....5....3....4....6....6....6....3....6....5....4....5....6....3....3....4
..5....4....4....7....4....5....5....5....5....4....6....7....7....5....7....5
..6....5....5....5....6....8....5....5....5....5....7....7....6....6....8....5
		

Links

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

Crossrefs

Column 3 of A250351.

Formula

Empirical: a(n) = 4*a(n-1) - 2*a(n-3) - 5*a(n-4) + a(n-6).

Empirical g.f.: x*(4 - 2*x^2 - 5*x^3 + x^5) / (1 - 4*x + 2*x^3 + 5*x^4 - x^6). - Colin Barker, Nov 12 2018