MathDB

Find permutations

Source: INMO 1992 Problem 4

October 4, 2005

permutationscountingcombinatorics

Problem Statement

Find the number of permutations

( p_1, p_2, p_3 , p_4 , p_5 , p_6)

1, 2 ,3,4,5,6

such that for any

k, 1 \leq k \leq 5

(p_1, \ldots, p_k)

does not form a permutation of

1 , 2, \ldots, k