Number of twin primes < 2^n.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =5a(5) =7a(6) =10a(7) =17a(8) =24a(9) =36a(10) =62a(11) =107a(12) =177a(13) =290a(14) =505a(15) =860a(16) =1526a(17) =2679a(18) =4750a(19) =8535a(20) =15500a(21) =27995a(22) =50638a(23) =92246a(24) =168617a(25) =309561a(26) =571313a(27) =1056281a(28) =1961080a(29) =3650557