a(n) = 2*a(n-2) + 2*a(n-3) for n >= 3, where a(0) = 2, a(2) = 4, a(3) = 7.

Terms

a(0) =2a(1) =4a(2) =7a(3) =12a(4) =22a(5) =38a(6) =68a(7) =120a(8) =212a(9) =376a(10) =664a(11) =1176a(12) =2080a(13) =3680a(14) =6512a(15) =11520a(16) =20384a(17) =36064a(18) =63808a(19) =112896a(20) =199744a(21) =353408a(22) =625280a(23) =1106304a(24) =1957376a(25) =3463168a(26) =6127360a(27) =10841088a(28) =19181056a(29) =33936896