Number of semiprimes <= 2^n.

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =10a(5) =22a(6) =42a(7) =82a(8) =157a(9) =304a(10) =589a(11) =1124a(12) =2186a(13) =4192a(14) =8110a(15) =15658a(16) =30253a(17) =58546a(18) =113307a(19) =219759a(20) =426180a(21) =827702a(22) =1608668a(23) =3129211a(24) =6091437a(25) =11868599a(26) =23140878a(27) =45150717a(28) =88157689a(29) =172235073