Partial sums of A076766.

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =31a(5) =63a(6) =131a(7) =279a(8) =621a(9) =1469a(10) =3766a(11) =10694a(12) =34728a(13) =133582a(14) =636719a(15) =3955451a(16) =33664265a(17) =407703531a(18) =7147333784a(19) =180948983492