a(n) = T(n,n-2), where T is the array in A026386.

Terms

a(0) =1a(1) =4a(2) =8a(3) =17a(4) =24a(5) =39a(6) =49a(7) =70a(8) =83a(9) =110a(10) =126a(11) =159a(12) =178a(13) =217a(14) =239a(15) =284a(16) =309a(17) =360a(18) =388a(19) =445a(20) =476a(21) =539a(22) =573a(23) =642a(24) =679a(25) =754a(26) =794a(27) =875a(28) =918a(29) =1005