a(n) = T(n,n-3), array T as in A055818.

Terms

a(0) =1a(1) =11a(2) =24a(3) =43a(4) =69a(5) =103a(6) =146a(7) =199a(8) =263a(9) =339a(10) =428a(11) =531a(12) =649a(13) =783a(14) =934a(15) =1103a(16) =1291a(17) =1499a(18) =1728a(19) =1979a(20) =2253a(21) =2551a(22) =2874a(23) =3223a(24) =3599a(25) =4003a(26) =4436a(27) =4899a(28) =5393a(29) =5919