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

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =12a(5) =26a(6) =45a(7) =75a(8) =112a(9) =164a(10) =225a(11) =305a(12) =396a(13) =510a(14) =637a(15) =791a(16) =960a(17) =1160a(18) =1377a(19) =1629a(20) =1900a(21) =2210a(22) =2541a(23) =2915a(24) =3312a(25) =3756a(26) =4225a(27) =4745a(28) =5292a(29) =5894