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

Terms

a(0) =0a(1) =1a(2) =6a(3) =19a(4) =42a(5) =79a(6) =132a(7) =205a(8) =300a(9) =421a(10) =570a(11) =751a(12) =966a(13) =1219a(14) =1512a(15) =1849a(16) =2232a(17) =2665a(18) =3150a(19) =3691a(20) =4290a(21) =4951a(22) =5676a(23) =6469a(24) =7332a(25) =8269a(26) =9282a(27) =10375a(28) =11550a(29) =12811