Number of (w,x,y,z) with all terms in {0,...,n} and |w-x|+|x-y+|y-z|=n.

Terms

a(0) =1a(1) =6a(2) =24a(3) =58a(4) =118a(5) =202a(6) =324a(7) =478a(8) =682a(9) =926a(10) =1232a(11) =1586a(12) =2014a(13) =2498a(14) =3068a(15) =3702a(16) =4434a(17) =5238a(18) =6152a(19) =7146a(20) =8262a(21) =9466a(22) =10804a(23) =12238a(24) =13818a(25) =15502a(26) =17344a(27) =19298a(28) =21422a(29) =23666