Partial sum of pi(k) from k = 1 to 2^n.

Terms

a(0) =1a(1) =5a(2) =19a(3) =61a(4) =203a(5) =669a(6) =2279a(7) =7797a(8) =27213a(9) =96111a(10) =343965a(11) =1240617a(12) =4513763a(13) =16546859a(14) =61027965a(15) =226454967a(16) =844181631a(17) =3161518957a(18) =11886015725a(19) =44847272299a(20) =169747439789a(21) =644345294711