Number of 0..n arrays x(0..3) of 4 elements with zero 3rd differences.

Terms

a(0) =4a(1) =9a(2) =22a(3) =41a(4) =66a(5) =107a(6) =158a(7) =219a(8) =304a(9) =403a(10) =516a(11) =661a(12) =824a(13) =1005a(14) =1226a(15) =1469a(16) =1734a(17) =2047a(18) =2386a(19) =2751a(20) =3172a(21) =3623a(22) =4104a(23) =4649a(24) =5228a(25) =5841a(26) =6526a(27) =7249a(28) =8010a(29) =8851