Index of 2^n in A381019.

Terms

a(0) =1a(1) =2a(2) =7a(3) =16a(4) =64a(5) =256a(6) =975a(7) =3856a(8) =16647a(9) =65039a(10) =260112a(11) =1044504a(12) =4177980a(13) =16777224