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

Terms

a(0) =0a(1) =1a(2) =8a(3) =33a(4) =88a(5) =197a(6) =380a(7) =673a(8) =1104a(9) =1721a(10) =2560a(11) =3681a(12) =5128a(13) =6973a(14) =9268a(15) =12097a(16) =15520a(17) =19633a(18) =24504a(19) =30241a(20) =36920a(21) =44661a(22) =53548a(23) =63713a(24) =75248a(25) =88297a(26) =102960a(27) =119393a(28) =137704a(29) =158061