Number of 3-almostprimes <= 2^n.

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =7a(5) =13a(6) =30a(7) =60a(8) =125a(9) =256a(10) =513a(11) =1049a(12) =2082a(13) =4214a(14) =8401a(15) =16771a(16) =33427a(17) =66550a(18) =132405a(19) =262865a(20) =522296a(21) =1036033a(22) =2055256a(23) =4075039a(24) =8078110a(25) =16008485a(26) =31720903a(27) =62847087a(28) =124501149a(29) =246638355