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) =8a(4) =28a(5) =74a(6) =159a(7) =304a(8) =528a(9) =860a(10) =1325a(11) =1960a(12) =2796a(13) =3878a(14) =5243a(15) =6944a(16) =9024a(17) =11544a(18) =14553a(19) =18120a(20) =22300a(21) =27170a(22) =32791a(23) =39248a(24) =46608a(25) =54964a(26) =64389a(27) =74984a(28) =86828a(29) =100030