Number of solutions to k_1 + 2*k_2 + ... + n*k_n = 1, where k_i are from {-1,0,1}, i=1..n.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =6a(5) =15a(6) =36a(7) =85a(8) =213a(9) =549a(10) =1423a(11) =3723a(12) =9882a(13) =26508a(14) =71579a(15) =194533a(16) =532120a(17) =1463561a(18) =4044075a(19) =11221727a(20) =31260192a(21) =87386579a(22) =245058185a(23) =689209348a(24) =1943530845a(25) =5494106583a(26) =15566303698a(27) =44196212866a(28) =125727934145a(29) =358317169828