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

Terms

a(0) =3a(1) =0a(2) =2a(3) =8a(4) =10a(5) =22a(6) =48a(7) =90a(8) =182a(9) =368a(10) =730a(11) =1462a(12) =2928a(13) =5850a(14) =11702a(15) =23408a(16) =46810a(17) =93622a(18) =187248a(19) =374490a(20) =748982a(21) =1497968a(22) =2995930a(23) =5991862a(24) =11983728a(25) =23967450a(26) =47934902a(27) =95869808a(28) =191739610a(29) =383479222