Half the number of 0..n arrays of length 7 with second differences nonzero.

Terms

a(0) =21a(1) =397a(2) =4379a(3) =22972a(4) =91482a(5) =284360a(6) =764297a(7) =1797975a(8) =3883755a(9) =7729696a(10) =14517156a(11) =25811656a(12) =44024953a(13) =72163603a(14) =114677011a(15) =176842932a(16) =266174946a(17) =391374778a(18) =564396617a(19) =798717009a(20) =1112552471a(21) =1525915970a(22) =2065331568a(23) =2759616340