zigzag1:=proc(n)
  uses ArrayTools;
  local i,u,v,a;
  u:=Replicate(<-1,1>,n):
  v:=Vector[row](1..n,i->i*(2*i-3)):
  v:=Reshape(<v+~1,v+~2>,2*n):
  a:=Matrix(n,n):
  for i to n do
    a[...,i]:=v[i+1..i+n];
    v+=u
  od:
  a
end:

zigzag2:=proc(n)
  local i,v,a;
  a:=zigzag1(n);
  v:=Vector(1..n-1,i->i^2);
  for i from 2 to n do
    a[n+2-i..n,i]-=v[1..i-1]
  od;
  a
end: