37442159domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumber of nonempty subsets of {1,2,...,n} in which exactly 1/2 of the elements are <= (n-1)/2.at n=28A047171Number of nonempty subsets of {1,2,...,n} in which exactly 1/2 of the elements are <= (n-2)/2.at n=27A047182a(n) = binomial(2*n + 2, n + 2) - 1.at n=13A322938Prime numbersat n=2287014