Binomial coefficient C(20,n).

Terms

a(0) =1a(1) =20a(2) =190a(3) =1140a(4) =4845a(5) =15504a(6) =38760a(7) =77520a(8) =125970a(9) =167960a(10) =184756a(11) =167960a(12) =125970a(13) =77520a(14) =38760a(15) =15504a(16) =4845a(17) =1140a(18) =190a(19) =20a(20) =1