a(n) = a(n-1)+a(n-2)+a(n-3)+(8*n^3-48*n^2+112*n-96)/3 with a(0)=0, a(1)=0 and a(2)=1.

Terms

a(0) =0a(1) =0a(2) =1a(3) =9a(4) =42a(5) =140a(6) =383a(7) =925a(8) =2056a(9) =4316a(10) =8705a(11) =17069a(12) =32810a(13) =62192a(14) =116743a(15) =217673a(16) =404000a(17) =747496a(18) =1380177a(19) =2544865a(20) =4688186a(21) =8631620a(22) =15886111a(23) =29230725a(24) =53776968a(25) =98926372a(26) =181971057a(27) =334716197a(28) =615660634a(29) =1132400520