A245949 Number of length n+3 0..7 arrays with some pair in every consecutive four terms totalling exactly 7.

2216, 13064, 73728, 397504, 2217096, 12257032, 67596992, 373997376, 2066660136, 11420014856, 63122102528, 348845096320, 1927940409608, 10655229621512, 58887811241024, 325454196462720, 1798683415254952, 9940745874984456

Offset

1,1

Links

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

Formula

Empirical: a(n) = 3*a(n-1) + 9*a(n-2) + 31*a(n-3) - 19*a(n-4) - 3*a(n-5) - 5*a(n-6) + a(n-7).

Empirical g.f.: 8*x*(277 + 802*x + 1824*x^2 - 1244*x^3 - 231*x^4 - 312*x^5 + 64*x^6) / (1 - 3*x - 9*x^2 - 31*x^3 + 19*x^4 + 3*x^5 + 5*x^6 - x^7). - Colin Barker, Nov 05 2018

Example

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

Crossrefs

Column 7 of A245950.

Sequence in context: A183831 A234867 A234862 * A223159 A223158 A241963

Adjacent sequences: A245946 A245947 A245948 * A245950 A245951 A245952

Keyword

nonn

Author

R. H. Hardin, Aug 08 2014

Status

approved