a(n) = a(n-1)+a(n-2)+a(n-3)+4*n^2-16*n+18 with a(0)=0, a(1)=0 and a(2)=1.

Terms

a(0) =0a(1) =0a(2) =1a(3) =7a(4) =26a(5) =72a(6) =171a(7) =371a(8) =760a(9) =1500a(10) =2889a(11) =5475a(12) =10266a(13) =19116a(14) =35435a(15) =65495a(16) =120832a(17) =222664a(18) =410017a(19) =754671a(20) =1388650a(21) =2554784a(22) =4699707a(23) =8644907a(24) =15901336a(25) =29248068a(26) =53796617a(27) =98948523a(28) =181995914a(29) =334743972