a(1)=2, a(2)=5, a(n)=2*a(n-1) + 5*a(n-2).

Terms

a(0) =2a(1) =5a(2) =20a(3) =65a(4) =230a(5) =785a(6) =2720a(7) =9365a(8) =32330a(9) =111485a(10) =384620a(11) =1326665a(12) =4576430a(13) =15786185a(14) =54454520a(15) =187839965a(16) =647952530a(17) =2235104885a(18) =7709972420a(19) =26595469265a(20) =91740800630a(21) =316458947585