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

Terms

a(0) =0a(1) =0a(2) =5a(3) =48a(4) =180a(5) =481a(6) =1034a(7) =1986a(8) =3441a(9) =5602a(10) =8623a(11) =12755a(12) =18126a(13) =25165a(14) =33951a(15) =44936a(16) =58367a(17) =74638a(18) =93934a(19) =116987a(20) =143760a(21) =175126a(22) =211253a(23) =252782a(24) =299884a(25) =353673a(26) =414098a(27) =482057a(28) =557997a(29) =642810