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

Terms

a(0) =0a(1) =1a(2) =12a(3) =57a(4) =168a(5) =395a(6) =792a(7) =1435a(8) =2400a(9) =3789a(10) =5700a(11) =8261a(12) =11592a(13) =15847a(14) =21168a(15) =27735a(16) =35712a(17) =45305a(18) =56700a(19) =70129a(20) =85800a(21) =103971a(22) =124872a(23) =148787a(24) =175968a(25) =206725a(26) =241332a(27) =280125a(28) =323400a(29) =371519