Smallest power of 2 that begins with n.

Terms

a(0) =1a(1) =2a(2) =32a(3) =4a(4) =512a(5) =64a(7) =8a(9) =1024a(11) =128a(12) =131072a(15) =16a(16) =17179869184a(19) =2048a(20) =2147483648