a(n) = T(n)^2 - n^2, where T(n) is a triangular number.

Terms

a(0) =0a(1) =0a(2) =5a(3) =27a(4) =84a(5) =200a(6) =405a(7) =735a(8) =1232a(9) =1944a(10) =2925a(11) =4235a(12) =5940a(13) =8112a(14) =10829a(15) =14175a(16) =18240a(17) =23120a(18) =28917a(19) =35739a(20) =43700a(21) =52920a(22) =63525a(23) =75647a(24) =89424a(25) =105000a(26) =122525a(27) =142155a(28) =164052a(29) =188384