Number of 0..5 arrays x(0..n) of n+1 elements with zero n-1st differences.

Terms

a(0) =1a(1) =6a(2) =12a(3) =26a(4) =58a(5) =108a(6) =202a(7) =394a(8) =468a(9) =848a(10) =2560a(11) =7740a(12) =11372a(13) =28356a(14) =20660a(15) =20032a(16) =68026a(17) =312678a(18) =662542a(19) =1536878a(20) =812306a(21) =461910a(22) =1466416a(23) =10325202