a(n) = Sum_{j=1..n} (3^j + (-2)^j).

Terms

a(0) =1a(1) =14a(2) =33a(3) =130a(4) =341a(5) =1134a(6) =3193a(7) =10010a(8) =29181a(9) =89254a(10) =264353a(11) =799890a(12) =2386021a(13) =7185374a(14) =21501513a(15) =64613770a(16) =193622861a(17) =581305494a(18) =1743042673a(19) =5230875650a(20) =15689131701a(21) =47074385614a(22) =141209175833a(23) =423655489530