Sum of squares of first n tribonacci numbers (A000213).

Terms

a(0) =1a(1) =2a(2) =3a(3) =12a(4) =37a(5) =118a(6) =407a(7) =1368a(8) =4617a(9) =15642a(10) =52891a(11) =178916a(12) =605325a(13) =2047726a(14) =6927407a(15) =23435376a(16) =79281105a(17) =268206130a(18) =907335091a(19) =3069492092a(20) =10384017717a(21) =35128880742a(22) =118840150983a(23) =402033352264