Index of 2^n-1 in A353709.

Terms

a(0) =0a(1) =1a(2) =5a(3) =53a(4) =76a(5) =245a(6) =1647a(7) =5257a(8) =20336a(9) =30940a(10) =124837a(11) =374756a(12) =1205149a(13) =2643792a(14) =7516934a(15) =29855796a(16) =102243621