A264551 Number of (2+1) X (n+1) arrays of permutations of 0..n*3+2 with each element having directed index change -1,1 -1,2 1,0 or 0,-1.

1, 2, 6, 16, 40, 96, 240, 608, 1536, 3840, 9600, 24064, 60416, 151552, 379904, 952320, 2387968, 5988352, 15015936, 37650432, 94404608, 236716032, 593559552, 1488322560, 3731881984, 9357492224, 23463460864, 58833502208, 147522060288

Offset: 1

Author

R. H. Hardin, Nov 17 2015

Keywords

• nonn

Examples

			Some solutions for n=4:
..1..2..6..4..8....1..5..3..4..8....1..5..3..7..8....1..2..5..4..8
..0.10.11..3.13....0.10..2.12.13....0.10..2.12..4....0..7.10..3.12
..5.12..7.14..9...11..6..7.14..9...11..6.13.14..9...11..6.13.14..9
		

Links

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

Crossrefs

Row 2 of A264550.

Formula

Empirical: a(n) = 2*a(n-1) + 8*a(n-4).

Empirical g.f.: x*(1 + 2*x^2 + 4*x^3) / (1 - 2*x - 8*x^4). - Colin Barker, Jan 08 2019