The number of prime-indexed primes below 2^n.

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =3a(5) =5a(6) =7a(7) =11a(8) =16a(9) =25a(10) =39a(11) =63a(12) =103a(13) =172a(14) =290a(15) =490a(16) =844a(17) =1464a(18) =2564a(19) =4522a(20) =8022a(21) =14325a(22) =25686a(23) =46382a(24) =84115a(25) =153327a(26) =280423a(27) =514798a(28) =948374a(29) =1752639