a(n) = A255448(2^n-1).

Terms

a(0) =1a(1) =5a(2) =19a(3) =71a(4) =257a(5) =925a(6) =3323a(7) =11919a(8) =42729a(9) =153173a(10) =549075a(11) =1968247a(12) =7055601a(13) =25292621a(14) =90668587a(15) =325028895a(16) =1165167673a(17) =4176914949a(18) =14973497539a(19) =53677355783a(20) =192423938625a(21) =689806295677