Number at end of segment n of A117073.

Terms

a(0) =3a(1) =6a(2) =11a(3) =22a(4) =42a(5) =84a(6) =168a(7) =336a(8) =672a(9) =1342a(10) =2684a(11) =5368a(12) =10736a(13) =21472a(14) =42944a(15) =85888a(16) =171776