A250321 Number of length 2+2 0..n arrays with the sum of second differences squared multiplied by some arrangement of +-1 equal to zero.

8, 25, 60, 117, 200, 321, 480, 681, 940, 1253, 1624, 2073, 2592, 3185, 3876, 4653, 5520, 6505, 7592, 8785, 10116, 11565, 13136, 14865, 16728, 18729, 20908, 23237, 25720, 28401, 31248, 34265, 37500, 40917, 44520, 48361, 52400, 56641, 61140, 65853, 70784

Offset

1,1

Comments

Row 2 of A250320.

Links

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

Formula

Empirical: a(n) = 2*a(n-1) - a(n-2) + 2*a(n-3) - 4*a(n-4) + 2*a(n-5) - a(n-6) + 2*a(n-7) - a(n-8).

Empirical g.f.: x*(8 + 9*x + 18*x^2 + 6*x^3 + 8*x^4 + 2*x^5 + 2*x^6 - x^7) / ((1 - x)^4*(1 + x + x^2)^2). - Colin Barker, Mar 19 2018

Example

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

Crossrefs

Cf. A250320.

Sequence in context: A270867 A360201 A004640 * A011924 A370081 A346522

Adjacent sequences: A250318 A250319 A250320 * A250322 A250323 A250324

Keyword

nonn

Author

R. H. Hardin, Nov 18 2014

Status

approved