A248431 Number of length n+2 0..6 arrays with every three consecutive terms having the sum of some two elements equal to twice the third.

61, 105, 185, 327, 601, 1105, 2021, 3761, 6969, 12815, 23897, 44337, 81597, 152209, 282457, 519895, 969849, 1799825, 3312853, 6180081, 11468921, 21110367, 39381145, 73083121, 134521133, 250947665, 465706137, 857206439, 1599109049, 2967610449

Offset: 1

Author

R. H. Hardin, Oct 06 2014

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 6 of A248433

Formula

Empirical: a(n) = 8*a(n-3) - 11*a(n-6) + 4*a(n-9).

Empirical g.f.: x*(61 + 105*x + 185*x^2 - 161*x^3 - 239*x^4 - 375*x^5 + 76*x^6 + 108*x^7 + 164*x^8) / ((1 - x)*(1 + x + x^2)*(1 - 7*x^3 + 4*x^6)). - Colin Barker, Nov 08 2018