21238169904domain: NAppears in sequencesa(n) = (n-1)*binomial(3*n-2,n)/(2*n-1) + (n+1)*binomial(3*n,n)/(2*n+1) - binomial(3*n-1,n).at n=15A262717Number of North-East lattice paths from (0,0) to (n,n) that cross the diagonal y = x horizontally exactly four times.at n=13A268447