Sequence and first differences include all positive integers except 2.

Terms

a(0) =1a(1) =4a(2) =9a(3) =15a(4) =22a(5) =30a(6) =40a(7) =51a(8) =63a(9) =76a(10) =90a(11) =106a(12) =123a(13) =141a(14) =160a(15) =180a(16) =201a(17) =224a(18) =248a(19) =273a(20) =299a(21) =326a(22) =354a(23) =383a(24) =414a(25) =446a(26) =479a(27) =513a(28) =548a(29) =584