a(n) = 3*a(n-1) + a(n-2) + n.

Terms

a(0) =1a(1) =4a(2) =15a(3) =52a(4) =175a(5) =582a(6) =1927a(7) =6370a(8) =21045a(9) =69514a(10) =229597a(11) =758316a(12) =2504557a(13) =8272000a(14) =27320571a(15) =90233728a(16) =298021771a(17) =984299058a(18) =3250918963a(19) =10737055966a(20) =35462086881a(21) =117123316630a(22) =386832036793