Number of odd semiprimes less than 2^n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =4a(6) =11a(7) =24a(8) =51a(9) =103a(10) =207a(11) =417a(12) =815a(13) =1622a(14) =3164a(15) =6210a(16) =12146a(17) =23711a(18) =46295a(19) =90307a(20) =176369a(21) =344155a(22) =672091a(23) =1312721a(24) =2565048a(25) =5013566a(26) =9804910a(27) =19183069a(28) =37547164a(29) =73526846