A229439 Number of n X 2 0..2 arrays with horizontal differences mod 3 never 1, vertical differences mod 3 never -1, and rows and columns lexicographically nondecreasing.
4, 7, 13, 25, 47, 84, 142, 228, 350, 517, 739, 1027, 1393, 1850, 2412, 3094, 3912, 4883, 6025, 7357, 8899, 10672, 12698, 15000, 17602, 20529, 23807, 27463, 31525, 36022, 40984, 46442, 52428, 58975, 66117, 73889, 82327, 91468, 101350, 112012, 123494
Offset: 1
Keywords
Examples
Some solutions for n=4: ..0..2....0..2....0..2....1..1....0..2....0..2....0..2....0..0....0..2....0..2 ..0..2....0..2....1..0....1..1....1..0....0..2....0..2....1..1....1..0....0..2 ..0..2....0..2....2..1....1..1....1..0....1..0....1..0....2..2....2..1....1..0 ..0..2....1..0....2..1....1..1....1..1....1..1....1..0....2..2....2..2....2..1
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Crossrefs
Column 2 of A229445.
Formula
Empirical: a(n) = (1/24)*n^4 + (1/12)*n^3 - (1/24)*n^2 + (23/12)*n + 2.
Conjectures from Colin Barker, Sep 16 2018: (Start)
G.f.: x*(4 - 13*x + 18*x^2 - 10*x^3 + 2*x^4) / (1 - x)^5.
a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5.
(End)
Comments