Number of -n..n arrays of 4 elements with first and second differences also in -n..n.

Terms

a(0) =25a(1) =175a(2) =651a(3) =1759a(4) =3899a(5) =7581a(6) =13405a(7) =22085a(8) =34421a(9) =51331a(10) =73815a(11) =102995a(12) =140071a(13) =186369a(14) =243289a(15) =312361a(16) =395185a(17) =493495a(18) =609091a(19) =743911a(20) =899955a(21) =1079365a(22) =1284341a(23) =1517229a(24) =1780429a(25) =2076491a(26) =2408015a(27) =2777755a(28) =3188511a(29) =3643241