def solution(n):
result = [[0] * n for i in range(n)]
answer = []
x, y, num = -1, 0, 1
for i in range(n):
for j in range(i,n):
if i % 3 == 0:
x += 1
elif i % 3 == 1:
y += 1
elif i % 3 == 2:
x -= 1
y -= 1
result[x][y] = num
num += 1
for i in result:
for j in i:
if j:
answer.append(j)
return answer