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) =18a(4) =60a(5) =138a(6) =297a(7) =528a(8) =912a(9) =1440a(10) =2200a(11) =3180a(12) =4536a(13) =6174a(14) =8330a(15) =10920a(16) =14144a(17) =17928a(18) =22599a(19) =27900a(20) =34300a(21) =41580a(22) =50094a(23) =59664a(24) =70848a(25) =83148a(26) =97344a(27) =113022a(28) =130732a(29) =150150