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

Terms

a(0) =0a(1) =1a(2) =13a(3) =56a(4) =158a(5) =365a(6) =725a(7) =1312a(8) =2198a(9) =3477a(10) =5245a(11) =7624a(12) =10742a(13) =14725a(14) =19725a(15) =25920a(16) =33470a(17) =42557a(18) =53397a(19) =66176a(20) =81150a(21) =98525a(22) =118533a(23) =141456a(24) =167606a(25) =197189a(26) =230509a(27) =267920a(28) =309726a(29) =356205