Number at start of segment n of A117073.

Terms

a(0) =1a(1) =4a(2) =9a(3) =20a(4) =40a(5) =82a(6) =166a(7) =334a(8) =670a(9) =1340a(10) =2682a(11) =5366a(12) =10734a(13) =21470a(14) =42942a(15) =85886a(16) =171774