735686domain: NAppears in sequencesa(n) = K_4(n) = Sum_{k>=0} A090285(4,k)*2^k*binomial(n,k). a(n) = 2*(n^4+14*n^3+62*n^2+91*n+21)/3.at n=29A090296a(1)=1, a(2)=2, a(n)=a(n-1)+floor(a(n-2)*a(n-1)/(a(n-2)+a(n-1))).at n=40A173090