Number of (w,x,y,z) with all terms in {1,...,n} and 2|w-x|<=n+|y-z|.

Terms

a(0) =0a(1) =1a(2) =16a(3) =75a(4) =236a(5) =567a(6) =1172a(7) =2157a(8) =3672a(9) =5861a(10) =8920a(11) =13031a(12) =18436a(13) =25355a(14) =34076a(15) =44857a(16) =58032a(17) =73897a(18) =92832a(19) =115171a(20) =141340a(21) =171711a(22) =206756a(23) =246885a(24) =292616a(25) =344397a(26) =402792a(27) =468287a(28) =541492a(29) =622931