matrix.py

def matrix(side_width):
    for y in xrange(side_width):
        for x in xrange(side_width):
            ring_number = min(x, y, side_width - 1 - x, side_width - 1 - y)
            ring_serial = x + y - 2 * ring_number

            if x >= y:
                ring_base = 4 * ring_number * (side_width - ring_number)
                result = ring_base + ring_serial
            else:
                ring_ceil = 4 * (ring_number + 1) * (side_width - ring_number - 1)
                result = ring_ceil - ring_serial

            sys.stdout.write('%6s' % (result + 1))
        sys.stdout.write('\n')

https://habrahabr.ru/post/210796/