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

1,1

Comments

Column 2 of A212782

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

Example

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

Crossrefs

Sequence in context: A106839 A044072 A044453 * A376144 A362528 A137019

Adjacent sequences: A212773 A212774 A212775 * A212777 A212778 A212779

Keyword

nonn

Author

R. H. Hardin May 27 2012

Status

approved