842688

Appears in sequences

• If X_1,...,X_n is a partition of a 2n-set X into 2-blocks then a(n) is equal to the number of 5-subsets of X containing none of X_i, (i=1,...n).at n=17A130811
• a(n) = v(n+1)/v(n), where v=A203527.at n=4A203528