Number of strings of numbers x(i=1..n) in 0..4 with sum i^2*x(i)^2 equal to n^2*16.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =15a(6) =31a(7) =119a(8) =555a(9) =2138a(10) =9548a(11) =33391a(12) =136682a(13) =468971a(14) =1753525a(15) =5789709a(16) =19745186a(17) =63565260a(18) =203046061a(19) =638284176a(20) =1947963410a(21) =5979604119a(22) =17725544038a(23) =53252284414a(24) =155128241215a(25) =456635560332