10539893domain: NAppears in sequencesa(n) = Sum_{k=0..floor(n/7)} binomial(n-4*k,3*k).at n=40A370722Expansion of 1/(1 - x^3*(1 + x)^4).at n=30A375318a(n) = Sum_{k=0..floor(2*n/7)} binomial(2*n-4*k,3*k).at n=20A392403