OFFSET
0,5
COMMENTS
The four walls of the castle are defended by n guards, each of whom is assigned to one of eight locations in the castle: one of the four towers at the corners of the castle, or the middle of one of the four walls. Each guard in a tower will defend the two adjoining walls, while each guard positioned at the middle of a wall will guard only that wall. The guards must be distributed so that each wall is defended by the same number of guards. If two distributions can be obtained from one another by reflection and/or rotation, they are counted as one.
LINKS
Martins Opmanis, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (1, 0, 1, 1, -2, 1, -3, 1, 0, -1, 3, -1, 2, -1, -1, 0, -1, 1).
FORMULA
G.f.: (1/((1 - x^6)*(1 - x^4)) + 1/((1 - x^3)*(1 - x^2))^2)/(2*(1 - x^4)). - Andrew Howroyd, May 29 2023
EXAMPLE
For n = 5 there are two distinct distributions:
2-0-0 1-1-0
| | | |
0 1 0 1
| | | |
0-1-1 1-0-1
PROG
(PARI) Vec((1/((1 - x^6)*(1 - x^4)) + 1/((1 - x^3)*(1 - x^2))^2)/(2*(1 - x^4)) + O(x^61)) \\ Andrew Howroyd, May 29 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Martins Opmanis, May 29 2023
EXTENSIONS
Terms a(22) and beyond from Andrew Howroyd, May 29 2023
STATUS
approved