Number of -n..n arrays x(0..2) of 3 elements with zeroth through 2nd differences all nonzero.

Terms

a(0) =2a(1) =36a(2) =142a(3) =376a(4) =778a(5) =1404a(6) =2294a(7) =3504a(8) =5074a(9) =7060a(10) =9502a(11) =12456a(12) =15962a(13) =20076a(14) =24838a(15) =30304a(16) =36514a(17) =43524a(18) =51374a(19) =60120a(20) =69802a(21) =80476a(22) =92182a(23) =104976a(24) =118898a(25) =134004a(26) =150334a(27) =167944a(28) =186874a(29) =207180