F derangements(n)
   [[Int]] r
   V perm = Array(0 .< n)
   L
      I all(enumerate(perm).map((indx, p) -> indx != p))
         r [+]= perm
      I !perm.next_permutation()
         L.break
   R r

F subfact(n) -> Int64
   R I n < 2 {1 - n} E (subfact(n - 1) + subfact(n - 2)) * (n - 1)

V n = 4
print(‘Derangements of ’Array(0 .< n))
L(d) derangements(n)
   print(‘  ’d)

print("\nTable of n vs counted vs calculated derangements")
L(n) 0.<10
   print(‘#2 #<6 #.’.format(n, derangements(n).len, subfact(n)))

n = 20
print("\n!#. = #.".format(n, subfact(n)))