a(n) = a(n-1)+a(n-2)+a(n-3)+4*n-8 with a(0)=0, a(1)=0 and a(2)=1.

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =14a(5) =32a(6) =67a(7) =133a(8) =256a(9) =484a(10) =905a(11) =1681a(12) =3110a(13) =5740a(14) =10579a(15) =19481a(16) =35856a(17) =65976a(18) =121377a(19) =223277a(20) =410702a(21) =755432a(22) =1389491a(23) =2555709a(24) =4700720a(25) =8646012a(26) =15902537a(27) =29249369a(28) =53798022a(29) =98950036