a(n) = the number of noncomposites (primes or 1) that are n digits long when written in binary.

Terms

a(0) =1a(1) =2a(2) =2a(3) =2a(4) =5a(5) =7a(6) =13a(7) =23a(8) =43a(9) =75a(10) =137a(11) =255a(12) =464a(13) =872a(14) =1612a(15) =3030a(16) =5709a(17) =10749a(18) =20390a(19) =38635a(20) =73586a(21) =140336a(22) =268216a(23) =513708a(24) =985818a(25) =1894120a(26) =3645744a(27) =7027290a(28) =13561907a(29) =26207278