a(0)=1, a(1)=2, a(2)=5, a(n) = 3*a(n+2) - a(n+3).

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =40a(5) =115a(6) =331a(7) =953a(8) =2744a(9) =7901a(10) =22750a(11) =65506a(12) =188617a(13) =543101a(14) =1563797a(15) =4502774a(16) =12965221a(17) =37331866a(18) =107492824a(19) =309513251a(20) =891207887a(21) =2566130837a(22) =7388879260a(23) =21275429893a(24) =61260158842a(25) =176391597266a(26) =507899361905