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

Terms

a(0) =0a(1) =0a(2) =4a(3) =16a(4) =56a(5) =132a(6) =279a(7) =504a(8) =880a(9) =1380a(10) =2125a(11) =3090a(12) =4392a(13) =6006a(14) =8134a(15) =10640a(16) =13824a(17) =17568a(18) =22113a(19) =27360a(20) =33700a(21) =40810a(22) =49247a(23) =58740a(24) =69696a(25) =81900a(26) =95992a(27) =111384a(28) =128968a(29) =148260