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

Terms

a(0) =0a(1) =1a(2) =5a(3) =12a(4) =25a(5) =41a(6) =66a(7) =94a(8) =132a(9) =176a(10) =229a(11) =285a(12) =359a(13) =436a(14) =522a(15) =617a(16) =727a(17) =840a(18) =971a(19) =1105a(20) =1257a(21) =1418a(22) =1588a(23) =1761a(24) =1964a(25) =2173a(26) =2391a(27) =2619a(28) =2865a(29) =3114