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

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =12a(5) =21a(6) =35a(7) =58a(8) =91a(9) =142a(10) =215a(11) =322a(12) =472a(13) =685a(14) =979a(15) =1385a(16) =1936a(17) =2684a(18) =3685a(19) =5023a(20) =6790a(21) =9119a(22) =12163a(23) =16130a(24) =21264a(25) =27887a(26) =36383a(27) =47249a(28) =61076a(29) =78621