32618domain: NAppears in sequences[ n(n-1)(n-2)(n-3)/11 ].at n=26A011921a(n) = a(n-1) + Sum_{k=0..floor(log_2(n-1))} a(2^k), a(1) = 1.at n=33A133147Triangle read by rows: T(n,k) is the number of relations from an n-element set to a k-element set that are not onto functions.at n=12A344116