A212776 Half the number of 0..2 arrays of length n+2 with second differences nonzero.

11, 27, 66, 162, 397, 973, 2385, 5846, 14329, 35122, 86088, 211011, 517211, 1267741, 3107372, 7616509, 18668898, 45759514, 112161581, 274920321, 673859821, 1651704234, 4048508001, 9923336574, 24323184920, 59618790539, 146132186103

Offset: 1

Author

R. H. Hardin May 27 2012

Keywords

• nonn

Comments

Column 2 of A212782

Examples

			Some solutions for n=5
..2....0....1....1....1....2....0....1....0....0....1....2....0....0....1....2
..0....2....1....2....1....2....1....2....2....2....2....1....2....0....0....0
..0....1....0....0....0....1....0....1....0....1....1....1....0....2....2....0
..1....2....0....1....1....1....2....2....0....2....2....2....2....1....0....2
..1....0....2....1....0....0....1....0....1....0....0....0....0....1....1....0
..2....1....1....0....2....0....2....1....0....2....2....1....2....0....0....1
..0....1....2....0....1....1....1....0....0....2....1....0....1....2....1....1
		

Links

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

Formula

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

Empirical: G.f. -x*(11+16*x+17*x^2+9*x^3) / ( -1+x+2*x^2+3*x^3+2*x^4 ). - R. J. Mathar, Jul 01 2013