A246480 Number of length 1+3 0..n arrays with no pair in any consecutive four terms totalling exactly n.

2, 10, 60, 172, 462, 966, 1880, 3256, 5370, 8290, 12372, 17700, 24710, 33502, 44592, 58096, 74610, 94266, 117740, 145180, 177342, 214390, 257160, 305832, 361322, 423826, 494340, 573076, 661110, 758670, 866912, 986080, 1117410, 1261162

Offset: 1

Author

R. H. Hardin, Aug 27 2014

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Row 1 of A246479.

Formula

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

Conjectures from Colin Barker, Nov 06 2018: (Start)

G.f.: 2*x*(1 + 2*x + 16*x^2 + 6*x^3 + 23*x^4) / ((1 - x)^5*(1 + x)^2).

a(n) = -n + 3*n^2 - 2*n^3 + n^4 for n even.

a(n) = -3 + 3*n + 3*n^2 - 2*n^3 + n^4 for n odd.

(End)