2 Apr
2005
2 Apr
'05
6:18 a.m.
Dan: Derangements are A000166. Dividing by factorials gives 1, 0, 1/2, 1/3, 3/8, 11/30, 53/144, 103/280, 2119/5760, 16687/45360, 16481/44800, 1468457/3991680, ... which is A053557/A053556, with references going back to Euler. Neil -------------------- Dan said:
Still: Neil -- if you're out there -- the disordered hats problem suggests two new sequences which a search on the word "derangement" did not find in the OEIS:
a) the numerators, and
b) the denominators
of the (always rational) probability (in lowest terms) that a random permutation of n items is a derangement.