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

Terms

a(0) =0a(1) =1a(2) =15a(3) =66a(4) =201a(5) =469a(6) =958a(7) =1735a(8) =2937a(9) =4656a(10) =7050a(11) =10242a(12) =14461a(13) =19813a(14) =26569a(15) =34904a(16) =45086a(17) =57293a(18) =71898a(19) =89050a(20) =109201a(21) =132534a(22) =159424a(23) =190167a(24) =225296a(25) =264966a(26) =309685a(27) =359823a(28) =415889a(29) =478142