3749001domain: NAppears in sequencesa(n) = Sum_{k <= n/2 } binomial(n-2k, 3k).at n=31A137356Number of compositions of 5*n-2 into parts 3 and 5.at n=18A369847a(n) = Sum_{k=0..floor((2*n+1)/3)} binomial(2*k+1,2*n-3*k+1).at n=22A391600