Arises in a coin-weighing problem.

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =11a(5) =20a(6) =41a(7) =82a(8) =163a(9) =334a(10) =659a(11) =1350a(12) =2667a(13) =5430a(14) =10763a(15) =21782a(16) =43307a(17) =87254a(18) =173867a(19) =349270a(20) =697003a(21) =1397590a(22) =2791595a(23) =5591382a(24) =11174571a(25) =22367574a(26) =44716715a(27) =89474390a(28) =178907819a(29) =357905750