Number of numbers <= 2^n that are the product of exactly four primes, not necessarily distinct.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =2a(5) =7a(6) =14a(7) =34a(8) =71a(9) =152a(10) =325a(11) =669a(12) =1405a(13) =2866a(14) =5931a(15) =12139a(16) =24782a(17) =50444a(18) =102458a(19) =207945a(20) =420511a(21) =850518a(22) =1716168a(23) =3460304a(24) =6968639a(25) =14022029a(26) =28189833a(27) =56631732a(28) =113697179a(29) =228115641