derangement 4 NB. task item 2
1 0 3 2
1 2 3 0
1 3 0 2
2 0 3 1
2 3 0 1
2 3 1 0
3 0 1 2
3 2 0 1
3 2 1 0
   (,subfactorial,#@derangement)"0 i.10  NB. task item 4
0      1      1
1      0      0
2      1      1
3      2      2
4      9      9
5     44     44
6    265    265
7   1854   1854
8  14833  14833
9 133496 133496
   subfactorial 20 NB. stretch task
8.95015e17
   subfactorial 20x NB. using extended precision
895014631192902121