login
A339798
Number of (undirected) Hamiltonian paths in the graph C_4 X C_n.
5
4128, 45696, 287160, 2172480, 11866848, 76468352, 390714840, 2301083680, 11288784144, 62812654272, 299720429528, 1604776566400, 7505573487360, 39105991164160, 180179056818584, 920223907284960, 4191443432295472, 21088555826121280, 95195388883597464, 473503955161244480
OFFSET
3,1
LINKS
Eric Weisstein's World of Mathematics, Hamiltonian Path
Eric Weisstein's World of Mathematics, Torus Grid Graph
PROG
(Python)
# Using graphillion
from graphillion import GraphSet
def make_CnXCk(n, k):
grids = []
for i in range(1, k + 1):
for j in range(1, n):
grids.append((i + (j - 1) * k, i + j * k))
grids.append((i + (n - 1) * k, i))
for i in range(1, k * n, k):
for j in range(1, k):
grids.append((i + j - 1, i + j))
grids.append((i + k - 1, i))
return grids
def A(start, goal, n, k):
universe = make_CnXCk(n, k)
GraphSet.set_universe(universe)
paths = GraphSet.paths(start, goal, is_hamilton=True)
return paths.len()
def B(n, k):
m = k * n
s = 0
for i in range(1, m):
for j in range(i + 1, m + 1):
s += A(i, j, n, k)
return s
def A339798(n):
return B(n, 4)
print([A339798(n) for n in range(3, 10)])
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 17 2020
STATUS
approved