複選題18. It is known that 12 + 22 + ... .+n2=n(n+1)(2n+1)/6.Let H(n)=(1+3)2 +(2+ 3)2+. + (n + 3)2. Which of the following are true about H(n)? (A) The constant term is not 0； (B) The coefficient of the term with n is ； (C) The coefficient of the term with n2 is ；(D) H(50) is greater than 50000.