A250271 Number of length n+1 0..2 arrays with the sum of the squares of adjacent differences multiplied by some arrangement of +-1 equal to zero.
3, 11, 27, 79, 255, 843, 2763, 8903, 28215, 88195, 272739, 836607, 2550735, 7742267, 23423355, 70695991, 213005415, 640982259, 1927141011, 5790335855, 17389881855, 52209491371, 156712360107, 470313240999, 1411308821655, 4234698216803, 12705705263043, 38120471232223
Offset: 1
Keywords
Examples
Some solutions for n=6: ..0....0....2....0....0....2....2....0....2....2....2....1....2....2....1....0 ..1....1....1....2....0....1....1....1....0....2....1....2....0....2....1....1 ..1....2....1....2....1....2....2....1....0....2....0....2....0....2....1....2 ..2....1....2....0....1....0....1....2....1....0....0....0....0....0....1....2 ..2....2....0....0....1....2....2....0....0....2....0....1....1....2....2....2 ..0....2....2....1....1....0....1....1....1....1....1....2....0....1....2....1 ..2....0....2....2....2....2....2....2....0....2....2....1....2....0....1....0
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Crossrefs
Column 2 of A250277.
Formula
Empirical: a(n) = 9*a(n-1) - 31*a(n-2) + 51*a(n-3) - 40*a(n-4) + 12*a(n-5) for n>6.
Conjectures from Colin Barker, Nov 12 2018: (Start)
G.f.: x*(3 - 16*x + 21*x^2 + 24*x^3 - 60*x^4 + 24*x^5) / ((1 - x)^2*(1 - 2*x)^2*(1 - 3*x)).
a(n) = 5*3^(n-1) - (2^n-2)*n for n>1. (End)
Comments