898129domain: NPropertiesPrimalityPrimeyesAppears in sequencesSum of the altitudes of the leftmost valleys of all Dyck paths of semilength n (if path has no valley, then this altitude is taken to be 0).at n=13A143955a(0) = 1 and a(n) = Sum_{k = 0..2*n} n/(n + 2*k)*binomial(n + 2*k,k) for n >= 1.at n=5A352275Prime numbersat n=71147