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

Terms

a(0) =1a(1) =2a(2) =3a(3) =8a(4) =27a(5) =78a(6) =219a(7) =649a(8) =1805a(9) =4987a(10) =13179a(11) =34331a(12) =87203a(13) =217281a(14) =532073a(15) =1278041a(16) =3025466a(17) =7046194a(18) =16192534a(19) =36706373a(20) =82197783a(21) =181900279a(22) =398099637a(23) =862217855a(24) =1848842707a(25) =3927404946a(26) =8267742253a(27) =17257223344a(28) =35726693834