Index of 2^n in A280864.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =13a(5) =30a(6) =65a(7) =127a(8) =258a(9) =530a(10) =1009a(11) =1988a(12) =3942a(13) =8004a(14) =16195a(15) =32389a(16) =64923a(17) =129870a(18) =260326a(19) =520787a(20) =1043257a(21) =2085202a(22) =4171403a(23) =8338443