OFFSET
1,2
MATHEMATICA
a[n_] := A271465[[2 n^2 - 2 n + 1]];
Table[a[n], {n, 1, 14}] (* Jean-François Alcover, Sep 23 2019 *)
PROG
(Python)
# Using graphillion
from graphillion import GraphSet
import graphillion.tutorial as tl
def A271507(n):
if n == 1: return 1
universe = tl.grid(n - 1, n - 1)
GraphSet.set_universe(universe)
start, goal = 1, n
paths = GraphSet.paths(start, goal)
return paths.len()
print([A271507(n) for n in range(1, 10)]) # Seiichi Manyama, Mar 21 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Apr 08 2016
STATUS
approved