G.f.: 1/(1 - x - 25*x^2).

Terms

a(0) =1a(1) =1a(2) =26a(3) =51a(4) =701a(5) =1976a(6) =19501a(7) =68901a(8) =556426a(9) =2278951a(10) =16189601a(11) =73163376a(12) =477903401a(13) =2306987801a(14) =14254572826a(15) =71929267851a(16) =428293588501