Partial sums of A000051, starting at n=1.

Terms

a(0) =3a(1) =8a(2) =17a(3) =34a(4) =67a(5) =132a(6) =261a(7) =518a(8) =1031a(9) =2056a(10) =4105a(11) =8202a(12) =16395a(13) =32780a(14) =65549a(15) =131086a(16) =262159a(17) =524304a(18) =1048593a(19) =2097170a(20) =4194323a(21) =8388628a(22) =16777237a(23) =33554454a(24) =67108887a(25) =134217752a(26) =268435481a(27) =536870938a(28) =1073741851a(29) =2147483676