Number of strings of numbers x(i=1..n) in 0..2 with sum i^2*x(i)^2 equal to n^2*4.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =4a(6) =4a(7) =7a(8) =19a(9) =47a(10) =71a(11) =207a(12) =474a(13) =1077a(14) =2262a(15) =4729a(16) =9770a(17) =18932a(18) =39277a(19) =75259a(20) =142407a(21) =269217a(22) =504234a(23) =930683a(24) =1699058a(25) =3071779a(26) =5553557a(27) =9841969a(28) =17407209a(29) =30656831