144535714domain: NAppears in sequencesa(n) = Sum_{k=0..floor(n/3)} binomial(n+3*k,n-3*k).at n=21A373905a(n) = Sum_{k=0..n} binomial(3*k,3*(n-k)).at n=14A391902a(n) = Sum_{k=0..floor(n/3)} binomial(2*n-3*k,3*k).at n=21A392402a(n) = Sum_{k=0..floor(2*n/3)} binomial(3*k,2*n-3*k).at n=21A392432