a(n) = A064688(n) - 1.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =11a(5) =17a(6) =37a(7) =53a(8) =103a(9) =255a(10) =339a(11) =759a(12) =1259a(13) =1609a(14) =2589a(15) =5119a(16) =9791a(17) =12075a(18) =22249a(19) =32991a(20) =40025a(21) =70487a(22) =101697a(23) =173681a(24) =345855a(25) =483329a(26) =570077a(27) =789639a(28) =927405a(29) =1274117