A070952(2^n-1).

Terms

a(0) =1a(1) =3a(2) =6a(3) =12a(4) =22a(5) =39a(6) =78a(7) =132a(8) =269a(9) =526a(10) =1036a(11) =2067a(12) =4162a(13) =8252a(14) =16387a(15) =32662a(16) =65372a(17) =130953a(18) =262212a(19) =524550a(20) =1047850a(21) =2097353a(22) =4192505a(23) =8384471