a(n) = 5*a(n-2) - 2*a(n-4), with initial terms 0,1,2,4.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =10a(5) =18a(6) =46a(7) =82a(8) =210a(9) =374a(10) =958a(11) =1706a(12) =4370a(13) =7782a(14) =19934a(15) =35498a(16) =90930a(17) =161926a(18) =414782a(19) =738634a(20) =1892050a(21) =3369318a(22) =8630686a(23) =15369322a(24) =39369330a(25) =70107974a(26) =179585278a(27) =319801226a(28) =819187730a(29) =1458790182