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

1,1

Links

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

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

Example

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

Crossrefs

Column 6 of A248433

Sequence in context: A086126 A023287 A203263 * A141919 A308797 A155571

Adjacent sequences: A248428 A248429 A248430 * A248432 A248433 A248434

Keyword

nonn

Author

R. H. Hardin, Oct 06 2014

Status

approved