Falls apart when the numbers get long

pascals_triangle.rb

rows = 8

t = []
rows.times do |i|
  t[i] = []
  (i+1).times do |j|
    if j == 0 || j == i
      t[i] << 1
    else
      t[i] << t[i-1][j-1] + t[i-1][j]
    end
  end
end

pt = t.map { |r| r.join(' ') }

pt.each do |r|
  puts r.center(pt.last.length)
end

# >>          1         
# >>         1 1        
# >>        1 2 1       
# >>       1 3 3 1      
# >>      1 4 6 4 1     
# >>    1 5 10 10 5 1   
# >>  1 6 15 20 15 6 1  
# >> 1 7 21 35 35 21 7 1