G.f.: 1/(1-5*x+10*x^3-5*x^4).

Terms

a(0) =1a(1) =5a(2) =25a(3) =115a(4) =530a(5) =2425a(6) =11100a(7) =50775a(8) =232275a(9) =1062500a(10) =4860250a(11) =22232375a(12) =101698250a(13) =465201250a(14) =2127983750a(15) =9734098125a(16) =44526969375a(17) =203681015625a(18) =931704015625