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

Terms

a(0) =0a(1) =1a(2) =9a(3) =36a(4) =106a(5) =252a(6) =528a(7) =964a(8) =1617a(9) =2559a(10) =3880a(11) =5631a(12) =7950a(13) =10900a(14) =14595a(15) =19161a(16) =24727a(17) =31419a(18) =39399a(19) =48790a(20) =59799a(21) =72570a(22) =87277a(23) =104124a(24) =123342a(25) =145075a(26) =169575a(27) =197061a(28) =227779a(29) =261915