a(0) = a(1) = 0; for n >= 2, a(n) = floor(sqrt(2^(n-2)-1)).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =1a(5) =2a(6) =3a(7) =5a(8) =7a(9) =11a(10) =15a(11) =22a(12) =31a(13) =45a(14) =63a(15) =90a(16) =127a(17) =181a(18) =255a(19) =362a(20) =511a(21) =724a(22) =1023a(23) =1448a(24) =2047a(25) =2896a(26) =4095a(27) =5792a(28) =8191a(29) =11585