Sum of generalized tribonacci numbers A001644 and inverted tribonacci numbers A075298.

Terms

a(0) =4a(1) =2a(2) =-2a(3) =12a(4) =12a(5) =10a(6) =54a(7) =68a(8) =108a(9) =282a(10) =422a(11) =772a(12) =1604a(13) =2674a(14) =5006a(15) =9580a(16) =16884a(17) =31506a(18) =58606a(19) =105948a(20) =196508a(21) =362298a(22) =662022a(23) =1222772a(24) =2249116a(25) =4127210a(26) =7605718a(27) =13984148a(28) =25701652a(29) =47311458