Arises in a coin-weighing problem.

Terms

a(0) =1a(1) =1a(2) =3a(3) =6a(4) =16a(5) =41a(6) =99a(7) =235a(8) =565a(9) =1347a(10) =3187a(11) =7515a(12) =17691a(13) =41523a(14) =97240a(15) =227361a(16) =530859a(17) =1237881a(18) =2883475a(19) =6710758a(20) =15606075a(21) =36268307a(22) =84239608a(23) =195567275a(24) =453832309a(25) =1052784046a(26) =2441461427a(27) =5660381126a(28) =13120263173a(29) =30405643251