Number of strings of numbers x(i=1..n) in 0..3 with sum i^2*x(i)^2 equal to n^2*9.

Terms

a(0) =1a(1) =1a(2) =2a(3) =1a(4) =5a(5) =5a(6) =41a(7) =36a(8) =199a(9) =420a(10) =1377a(11) =4140a(12) =10728a(13) =36839a(14) =87400a(15) =283225a(16) =660812a(17) =1940633a(18) =4609045a(19) =12276261a(20) =29878104a(21) =73822900a(22) =181872899a(23) =428160287a(24) =1053371836a(25) =2416581766a(26) =5864707345a(27) =13309989382a(28) =31614183273a(29) =71451195226