Number of (w,x,y,z) with all terms in {1,...,n} and w=x+2y+3z-n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =11a(6) =21a(7) =37a(8) =59a(9) =88a(10) =125a(11) =172a(12) =228a(13) =296a(14) =376a(15) =469a(16) =576a(17) =699a(18) =837a(19) =993a(20) =1167a(21) =1360a(22) =1573a(23) =1808a(24) =2064a(25) =2344a(26) =2648a(27) =2977a(28) =3332a(29) =3715