353452638000domain: NAppears in sequencesConsider all compositions (ordered partitions) of n into n parts, allowing zeros. E.g., for n = 3 we get 300, 030, 003, 210, 120, 201, 102, 021, 012, 111. Then a(n) is the total number of 1's.at n=19A097070a(n) = sigma(n) * binomial(2*n-1,n), for n >= 1.at n=18A357552