a(n) = a(n-1)+4*a(n-2)-4*a(n-4).

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =6a(5) =10a(6) =30a(7) =62a(8) =158a(9) =366a(10) =878a(11) =2094a(12) =4974a(13) =11886a(14) =28270a(15) =67438a(16) =160622a(17) =382830a(18) =912238a(19) =2173806a(20) =5180270a(21) =12344174a(22) =29416302a(23) =70097774a(24) =167041902a(25) =398056302a(26) =948558702a(27) =2260392814a(28) =5386460014a(29) =12835806062