Number of (w,x,y,z) with all terms in {1,...,n} and w+x=3y+3z.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =3a(5) =9a(6) =16a(7) =26a(8) =44a(9) =63a(10) =87a(11) =123a(12) =160a(13) =204a(14) =264a(15) =325a(16) =395a(17) =485a(18) =576a(19) =678a(20) =804a(21) =931a(22) =1071a(23) =1239a(24) =1408a(25) =1592a(26) =1808a(27) =2025a(28) =2259a(29) =2529