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

Terms

a(0) =1a(1) =3a(2) =12a(3) =20a(4) =45a(5) =63a(6) =112a(7) =144a(8) =225a(9) =275a(10) =396a(11) =468a(12) =637a(13) =735a(14) =960a(15) =1088a(16) =1377a(17) =1539a(18) =1900a(19) =2100a(20) =2541a(21) =2783a(22) =3312a(23) =3600a(24) =4225a(25) =4563a(26) =5292a(27) =5684a(28) =6525a(29) =6975