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

Terms

a(0) =0a(1) =0a(2) =3a(3) =10a(4) =25a(5) =49a(6) =86a(7) =137a(8) =206a(9) =294a(10) =405a(11) =540a(12) =703a(13) =895a(14) =1120a(15) =1379a(16) =1676a(17) =2012a(18) =2391a(19) =2814a(20) =3285a(21) =3805a(22) =4378a(23) =5005a(24) =5690a(25) =6434a(26) =7241a(27) =8112a(28) =9051a(29) =10059