import random

def in_center(node, n):
    return node > n - 1 and node % n != 0 and (node + 1) % n != 0 and node < n*(n-1)

n = 4
nodes = []
operations = [n, -n, 1, -1]

center_nodes = []
for i in range(0, n*n):
    if in_center(i, n):
       center_nodes.append(i)
node = random.choice(center_nodes)
nodes.append(node)
while in_center(node, n):
    operation = random.choice(operations)
    next_node = node + operation
    if next_node > 0 and next_node < n * n and next_node not in nodes:
        nodes.append(next_node)
        node = next_node

print(nodes)