Number of 0..n arrays x(0..5) of 6 elements with zero 3rd differences.

Terms

a(0) =2a(1) =3a(2) =6a(3) =9a(4) =14a(5) =25a(6) =36a(7) =47a(8) =64a(9) =87a(10) =110a(11) =143a(12) =176a(13) =209a(14) =258a(15) =311a(16) =364a(17) =431a(18) =498a(19) =575a(20) =666a(21) =761a(22) =856a(23) =969a(24) =1092a(25) =1219a(26) =1364a(27) =1513a(28) =1662a(29) =1847