m.rb

def m(n)
  seq = (0..n/2).to_a
  res = []
  seq.each do |e|
    r = (0..e).to_a
    r << r.last while r.length < seq.length
    res << r + r.reverse.drop(1)
  end
  res + res.reverse.drop(1)
end

m(7).each do |e|
  p e
end

[0, 0, 0, 0, 0, 0, 0]
[0, 1, 1, 1, 1, 1, 0]
[0, 1, 2, 2, 2, 1, 0]
[0, 1, 2, 3, 2, 1, 0]
[0, 1, 2, 2, 2, 1, 0]
[0, 1, 1, 1, 1, 1, 0]
[0, 0, 0, 0, 0, 0, 0]